Chrysotile is a fibrous mineral that belongs to the serpentine mineral group. Other members of the group are lizardite and antigorite. All serpentine group minerals share the same chemical composition (Mg₃Si₂O₅(OH)₄) but they have different crystal structures. Chrysotile is the only one among them with a fibrous habit.

Chrysotile occurs as cross-cutting veins in serpentinized rocks. Serpentinization is a hydrothermal (temperature below 350 °C¹) metamorphic process that affects magnesium-rich igneous rocks like peridotite and pyroxenite. These are rocks that contain lots of olivine and pyroxene. These minerals are altered to serpentine group minerals plus magnetite. Magnetite forms because ultramafic igneous rocks contain lots of iron but serpentine group minerals contain no iron at all. So the iron just has to form its own phase. This is the reason why serpentine minerals often seem to be weakly magnetic. They are not but they usually contain lots of small magnetite crystals.

Most serpentinites form in the oceanic crust which is heated from below and percolated by ocean water. Obduction of such rocks accounts for serpentinites squeezed between continental blocks. Such former pieces of oceanic lithosphere which are now part of the continental lithosphere are known as ophiolite complexes.

Chrysotile aggregate is composed of many parallel long and very thin rolled tubes of chrysotile sheets. Each tube is about 20 nanometers thick. It is far too thin to be seen with the unaided eye. The fibers that we see are actually aggregates of many parallel rolled tubes. The length of the tubes is variable but may be up to several centimeters. Chrysotile forms rolled tubes because their crystal structure is composed of two layers, one of them being slightly smaller. This difference is compensated by rolling the sheet so that the shorter sheet remains inside.

Chrysotile asbestos and associated health hazards

Chrysotile is the most commonly used asbestos mineral although its golden days are clearly over because of health concerns. Asbestos minerals do not form a single mineralogical whole. Most of them are amphiboles. Chrysotile is the only non-amphibole asbestiform mineral. This is why it perhaps deserves to be treated separately from other asbestos minerals. Grouping them all together is a dubious practice, at best, that simply demonstrates a lack of scientific literacy.

The health risks associated with asbestos are very real but one should be able to make a clear difference between serpentine and amphibole groups which are most likely not equally hazardous. Another aspect that seems to be poorly understood is that pulmonary disease may develop as a result of intensive and long-term exposure to asbestos fibers in the air. Chrysotile or white asbestos as it is frequently called is likely not as hazardous substance as it is usually imagined to be.

The reason why people are so afraid of it is in my opinion their ignorance. They simply don’t know what it is — have never seen, have no personal experience. Perhaps they even don’t know that this is a natural material. The situation is somewhat similar to nuclear energy which is also very dangerous stuff if handled the wrong way. However, in my opinion it is really the only serious alternative to fossil fuels at the moment. Unfortunately, the scientifically illiterate public just do not understand what are atoms and how on earth they can be used to make electricity. They can not see nor sense radiation and are therefore frightened and don’t want to know anything more about it. I guess most people have no idea that we are all the time exposed to radiation. The same seems to be true with particulate mineral matter. Our bodies are under constant biological and mineralogical attack but we are not that easily knocked out. Our immune system and repair mechanisms are effective and can cope with most of the dangers. It is extremely unlikely that we have not developed an adequate defense against low-level exposure to mineral dust, fibrous or not.

I already mentioned fossil fuels and nuclear energy. There is one more thing that I would like to say about it. The current situation in the world proves that there really are no serious alternatives to fossil fuels. We have postponed or cancelled lots of nuclear energy projects in many countries after the Fukushima accident and as a result our appetite for shale gas, tar sand, oil shale, and coal are going straight up. I don’t want to think what it means to our climate. I have actually largely given up worrying about that because firstly, I can not do anything about it and secondly, I will be dead before the situation gets really bad. It was ironic and desperate remark. I do actually feel responsibility but to my grandchildren who might ask why did you (I mean the mankind living today) do it I simply say that I am not powerful enough to alter the course we as a human race have chosen to follow. I wrote my blog to educate people but only a handful of them read that. And those who read already knew it all. People that should read and learn are unfortunately not doing it. So my impact is almost nil anyway and I guess that blogging won’t count as an excuse, unfortunately.

Properties and uses of chrysotile

Chrysotile has been extensively used in the past because it has many useful properties. It is a good thermal and electrical insulator. It also absorbs sound and is chemically inert. Chrysotile is fire-resistant and absorbs mechanical energy. Its fibers are flexible with enough tensile strength to be woven. It is perhaps needless to say that it was once considered to be an almost ideal material for hundreds of versatile industrial applications.

http://picasaweb.google.com/107509377372007544953/Rocks#5850409755054232642
Lots of chrysotile veins in serpentinite from Tuva near Mongolia. Width of sample is 9 cm.

References

1. Baronnet, Alain J. (2007). Chrysotile rock. In: McGraw Hill Encyclopedia of Science & Technology, 10th Edition. McGraw-Hill. Volume 4. 151-153.

Smoky quartz is a light brown to black variety of quartz. Black smoky quartz is known as morion. Smoky quartz is a normal quartz in almost every sense. It just has an odd color but this is caused by a very small amount of impurities. All natural crystals contain impurities, this is no reason to define them as separate minerals. But what is the cause of this coloration?

http://picasaweb.google.com/107509377372007544953/Rocks#5842989770630082594
Large crystal of smoky quartz from Ukraine. Quartz has no cleavage, hence the fracture surface is without planar surfaces. Width of sample is 11 cm.

There is a rather complicated theory behind it. The question is still being studied but some things seem to be clear. First, it has been shown experimentally that we need radiation to change the color. Smoky quartz crystals did not look that way after the formation. Their color was altered slowly. Second, we need color centers. These are several metal ions that occur accidentally within quartz crystals.

There are most likely several different ions involved because light needs to be absorbed in many different wavelengths to result in a fuzzy smoky hue. Studies have shown that the most likely candidates are manganese, aluminum, and titanium ions. The article about smoky quartz in Wikipedia says that the coloration is a result of free silicon in the lattice but I am very sceptical about this interpretation.

http://picasaweb.google.com/107509377372007544953/Rocks#5847099161321565506
Morion is a black quartz. This large crystal (12 cm) shows crystal faces typical to quartz.
http://picasaweb.google.com/107509377372007544953/Rocks#5847099160896443730
Another side of the same crystal demonstrates typical conchoidal fracture of quartz.

Pyrite is the most abundant and widespread sulfide mineral (FeS₂). It rarely makes up the bulk of the rock, but it frequently occurs in rocks. It is a common mineral in sedimentary rocks, especially if they contain or contained organic matter. It is also a very common hydrothermal mineral. Few hydrothermal veins are without it. Especially common association is pyrite with quartz.

http://picasaweb.google.com/107509377372007544953/Rocks#5806175583309801394
Sedimentary rock shale containing cubes of pyrite and veins of quartz. Width of sample 8 cm. TUG 1608-2799.

Pyrite is an iron sulfide. Sulfur managed to combine with iron because its strongest competitor oxygen was nowhere to be found. Oxygen was consumed by decomposing organic matter or maybe we should say it the other way around: oxygen was busy destroying the organic stuff and lost its freedom in the process. This is why we often find it in coal and black shales. They both contain organic matter that was preserved because there were not enough oxygen available to destroy it all. This also gave chance to pyrite.

Hydrothermal pyrite has been frequently mistaken for gold and therefore the name fool’s gold. It is much more common than gold and it is not very difficult to tell them apart. Pyrite is a hard mineral (Mohs hardness over 6) but gold is soft. It is easy to scratch pure gold with a knife or needle. You can not do it with pyrite. Its crystals are brittle but gold is malleable.

Also the color is different. Gold is bright golden yellow, but pyrite is somewhat paler or even greenish yellow. In powdered form is greenish black. This is the color of a streak pyrite leaves on a streak plate. It is also significantly lighter in weight. Specific weights are about 5 and over 19 for pyrite and gold, respectively. However, despite the large difference, this property is not very useful to differentiate them because it is not very likely to find gold nuggets large enough to really feel their weight. Gold nuggets have a characteristic irregular and somewhat rounded shapes which is the result of their malleability. Pyrite is also irregular, but the cubic outline of individual crystals should be noticeable.

It is much harder to tell it apart from other similar sulfides like chalcopyrite, pyrrhotite, and marcasite. Chalcopyrite (CuFeS₂) is brighter in color and softer (can be scratched by a knife). These two often occur together and if there is enough chalcopyrite they may be mined together as an ore of copper. Pyrrhotite is usually magnetic, darker in color and also scratched by a knife. The only real problem is marcasite. These minerals sometimes have a different habit but in many cases XRD analysis is needed to be sure.

Pyrite is not resistant in the weathering environment. It fairly quickly breaks up in contact with oxygen and water. This reaction oxidizes the iron and releases sulfur as a sulfuric acid. This reaction has given it a negative reputation as an environmentally very problematic mineral. This process is of course entirely natural and won’t cause significant problems in itself but in combination with mining (as an acid mine drainage) things can get a lot nastier. Acidic water pumped out or leaked from mines has a negative impact on ecosystems. It is not only harmful because of acidity, but also because acidic water carries lots of dissolved heavy metals. Many of which are harmful and eventually make their way to our food supply. The decomposition of pyrite is an exothermal process (heat is released) which means that mining dump heaps containing it may ignite spontaneously. Such subterranean fires release harmful compounds to the groundwater and are exceedingly difficult to put out. Water does not help, this is what pyrite needs to decompose and it is also foolish to open up burning hills because it will only bring in more oxygen. Hence, pyrite is a significant environmental headache and is one of the most important reasons why we often say that most fossil fuels are “dirty”.

Pyrite may have a negative reputation as an unwanted impurity in fossil fuels, but it is also mined as a mineral resource. It is composed of two chemical elements — sulfur and iron, which both have lots of industrial applications. However, it is usually is mined for its sulfur content. Banded iron formations which usually contain iron as oxides (magnetite, hematite) are much better ores of iron. Sulfur extracted from pyrite is mostly used to make sulfuric acid which has many industrial applications. Because of that it is said that the amount of sulfuric acid produced is a good indicator of country’s industrial strength. Sulfuric acid is used to make fertifizers, detergents, explosives, batteries, pharmaceuticals, etc.

Pictures

http://picasaweb.google.com/107509377372007544953/Rocks#5806175545260398674
Crystals from Cyprus (the Troodos ophiolite). Such formation is known as VMS (volcanogenic massive sulfide).The mineral precipitated out of hot hydrothermal vents (black smokers) near the mid-ocean ridges. These deposits must be very widespread in the oceanic crust, but they only occasionally get squeezed between continental landmasses and become available to us.

It is often together with chalcopyrite and the minerals are therefore mined together. Chalcopyrite as a principal ore of copper is much more useful. Pyrite is paler yellow, chalcopyrite has more intense color. Width of sample 8 cm. Hannukainen, Finland.

http://picasaweb.google.com/107509377372007544953/Cyprus2#5737565800616120706
Large boulder of massive sulfide from Cyprus. It is called massive because it is indeed full of pyrite and contains little else. Here is an example of pyrite as a rock type.
http://picasaweb.google.com/107509377372007544953/Cyprus2#5737567417400375058
This sample of basalt, pyrite and quartz is part of a stockwork below the the massive sulfide lens in Cyprus. This is basaltic seafloow through which hot and metal-bearing water rose to form massive deposits on the seafloor above.
http://picasaweb.google.com/107509377372007544953/Cyprus2#5737568019351881474
Beautiful but toxic. Acidic water filling former VMS mine in Cyprus.
http://picasaweb.google.com/107509377372007544953/Rocks#5850032480050062514
Pyrite cubes and quartz in a vein that cuts through quartzitic rock. Width of sample is 11 cm.
http://picasaweb.google.com/107509377372007544953/Rocks#5806175599415189458
Pyrite is afraid of water and oxygen but nature is full of surprises. Here is a beach sand in Cyprus that is largely composed of pyrite cubes (reddish part of the beach).
http://picasaweb.google.com/107509377372007544953/Rocks#5806175732205917090
Sand sample from the same beach. Crystals are reddish because they are weathered (covered by goethite).
http://picasaweb.google.com/107509377372007544953/Rocks#5806175690899197394
Disseminated pyrite in andesitic igneous rock. Southern Ireland. Width of view 10 cm.
http://picasaweb.google.com/107509377372007544953/Rocks#5806175603520948850
Veins of pyrite and quartz in andesite in Southern Ireland.
http://picasaweb.google.com/107509377372007544953/Rocks#5806175687884966690
Close-up of the same vein. Both minerals are very common in hydrothermal veins.
http://picasaweb.google.com/107509377372007544953/Rocks#5806175718123213698
Rounded aggregates from Estonian carbonate sedimentary rocks. Width of view 5 cm.

Andalusite is an aluminum-rich silicate mineral. Andalusite is a common mineral in aluminum-bearing metamorphic rocks. It forms at low to medium temperatures and pressures. It is trimorphous with sillimanite and kyanite. It means that these three minerals have the same chemical composition, but they have different crystalline structure and therefore quite different appearance. The chemical composition of these three minerals are often expressed the following way: Al₂SiO₅ but not always. Sometimes it is written as AlAlOSiO₄ or Al₂OSiO₄ to show that they are orthosilicates.

http://picasaweb.google.com/107509377372007544953/Rocks#5802927328818088386
Andalusite crystals are often large enough to be seen with the naked eye and have a characteristic square-shaped cross-section. Mn-rich variety from The Vosges Mountains, France. The width of the cross-section of the largest crystal is 16 mm.

Orthosilicates are silicate minerals which possess isolated silica tetrahedra (SiO₄) in their crystal structure. These tetrahedra are like three-dimensional islands surrounded by other elements. Other well-known orthosilicates are zircon, olivine, garnet, topaz, titanite, etc. These are the least siliceous minerals among the silicate minerals and their chemical formula is usually written in the way which clearly shows isolated silica tetrahedra as an important structural unit. If we write the chemical formula as Al₂SiO₅, then we set these three silicates artificially apart from their relatives.

Andalusite, kyanite, and sillimanite have quite distinctive appearance from each other. Andal. crystals (they are commonly large enough to be seen) are elongated and have almost square cross-section. Kyanite is also elongated, but it is bladed and often has a distinctive bright blue color. Sillimanite is usually fine-grained, crystals are elongated as well, sometimes fibrous (variety known as fibrolite).

Andalusite is usually pink but white, gray, yellow, green (greenish gray), and violet varieties also occur frequently. Variation of color is mostly due to chromophore elements. Iron gives pink coloration, manganese is responsible for greenish hue¹. Andalusite is usually relatively pure, but it may contain manganese and iron (both are chromophores) that replace aluminum in the lattice. Andalusite variety chiastolite contains dark carbonaceous inclusions that form a cross along the diagonals of the prism. Andalusite may easily alter to sericite (fine-grained muscovite) or to other sheet silicates. Variety chiastolite is especially prone to such alteration which starts from the contact surface between andalusite and carbonaceous inclusions¹. Other inclusions like quartz, opaque minerals, and other minerals are also common in the crystals but they are small, visible with a microscope only. Andalusite is physically hard mineral (7.5 on Mohs scale), but it may be less on the surface because of alteration⁴.

http://picasaweb.google.com/107509377372007544953/Rocks#5802927328912521090
Porphyroblasts of andal. variety chiastolite (note diagonal dark zones) in a metamorphosed claystone from Germany. Chiastolitic cruciform pattern (visible when crystals are cut at right angles to the longest axis of the prism) forms because growing andalusite crystal pushes impurities aside as it grows. Initially in was unable to free itself from all types of inclusions, but as the crystals grow bigger they become more and more clear¹. Width of sample 11 cm.

Andalusite occurs chiefly in metamorphic rocks. These metamorphic rocks are rich in aluminum. The protoliths are sedimentary rocks that consequently also have to contain lots of aluminum. These are sedimentary rocks that are rich in clay (shale, argillite, mudstone, etc.). All clay minerals contain lots of aluminum. It is the least dense of the three polymorphs (andalusite, kyanite, sillimanite) and is therefore stable at lower pressure. If pressure rises, andalusite transforms to kyanite. If temperature rises much faster than pressure, then sillimanite is the most stable of the three. All of them occur in metamorphic rocks which makes them very good indicators of the metamorphic conditions during their formation. Andalusite is no longer stable if the temperature rises approximately above 600 °C and the pressure over 4 kbar (diagram below) which equals about 12…14 km depth in the crust.

Andalusite is a common mineral in hornfels. Hornfels is a fine-grained metamorphic rock formed by contact metamorphism – baked sedimentary rock next to hot magma intrusion. It is also common in regionally metamorphosed (related to mountain-building events) rocks like slate and mica schist and may occasionally occur in granitic igneous rocks. Andalusite is not particularly stable in the weathering environment, but it may be found in sand and sandstone if low to medium grade metamorphic rocks are not too far away. Andalusite and kyanite are used as a refractory source material. They are heated to produce mullite (andal. needs to be heated to 1450…1500 °C) which is used to make bricks resistant to high temperature and other fire-resistant materials (in spark plugs³, for example). Sillimanite is rarely used for that purpose because it tends to be too fine-grained which makes it difficult to extract sillimanite from rocks and it requires higher temperature to mullitize. Largest commercial deposits are in South Africa. Transparent crystals may serve as gemstones. Andalusite was first described in Andalusia (Spain), and was named after this region⁴.

http://picasaweb.google.com/107509377372007544953/Rocks#5803213760299186690
Stability fields of aluminum silicates². Andalusite is stable at low pressure and temperature. 1 kbar equals roughly 3.5 km depth in the continental crust.

References

1. Deer, W. A., Howie, R. A. & Zussman, J. (1996). An Introduction to the Rock-Forming Minerals, 2nd Edition. Prentice Hall.
2. Nesse, William D. (2011). Introduction to Mineralogy, 2nd Edition. Oxford University Press.
3. Klein, C., Hurlbut, C. S. (1993). Manual of Mineralogy, 21st Edition. John Wiley & Sons.
4. Hurlbut, C. S. (2007). Andalusite. In: McGraw Hill Encyclopedia of Science & Technology, 10th Edition. McGraw-Hill. Volume 1. 652-653.

Riebeckite is an amphibole group mineral. Amphiboles are hydrous silicate minerals. They are widespread in metamorphic and igneous rocks. Amphibole crystals are elongated because of their crystal structure which is composed of parallel silicate chains.

http://picasaweb.google.com/107509377372007544953/Rocks#5801027597794169954
Crystals in pegmatite (alkali feldspar granite according to the QAPF classification). Gray mineral is quartz. Colorado, USA. Width of sample 7 cm.

The most common amphibole mineral by far is hornblende. Riebeckite is a sodic amphibole (rich in Na). It forms a solid solution series with another sodic amphibole glaucophane. The chemical formula of the glaucophane-riebeckite pair:

Na₂Mg₃Al₂Si₈O₂₂(OH)₂ (glaucophane) — Na₂Fe₃²⁺Fe₂³⁺Si₈O₂₂(OH)₂ (riebeckite)

Both of them contain sodium, but magnesium and aluminum of glaucophane are replaced with iron in riebeckite which gives it much darker color. Both of them are bluish, but macroscopic riebeckite crystals are so dark that they are practically black. There is also a solid solution towards other less common sodium-bearing amphibole group minerals like arfvedsonite and richterite. Amphiboles are very complex minerals because of numerous replacements in their crystal structures. Their complexity is perhaps comparable to clay minerals only. The dividing line between them is an arbitrary 50% of Fe³⁺ content. The nomenclature used to be even more complicated because the composition between the two end-members (Fe³⁺ content between 30…70%) was referred to as crossite. This usage is obsolete since 2003¹.

Riebeckite commonly forms prismatic crystals, but it also occurs as a fibrous asbestiform mineral. Asbestiform variety is known as crocidolite or blue asbestos. This infamous variety of riebeckite used to have many applications, but it is no longer used in most countries. Crocidolite is considered to be one of the most hazardous of asbestiform minerals. The fibers of blue asbestos have greater tensile strength but lower heat resistance than chrysotile fibers² which belong to the serpentine mineral group. Chrysotile is the most commonly used asbestiform mineral. Fibrous riebeckite which is partially replaced by quartz is known as tiger eye. It is widely used in lapidary work.

This mineral is found in alkali-rich igneous rocks such as alkali granite, syenite, nepheline syenite, and some acidic Na-rich volcanic rocks. Crocidolite occurs in metamorphosed iron formations. Glaucophane occurs in low-temperature, high-pressure metamorphic rocks (former basalt in subducting slabs).

http://picasaweb.google.com/107509377372007544953/Coll#5779170714655278658
A sample of blue asbestos crocidolite (fibrous riebeckite) from South Africa showing the fibrous nature of the mineral. Width of sample 3 cm.

References

1. Nesse, William D. (2011). Introduction to Mineralogy, 2nd Edition. Oxford University Press.
2. Deer, W. A., Howie, R. A. & Zussman, J. (1996). An Introduction to the Rock-Forming Minerals, 2nd Edition. Prentice Hall.

Halite is a mineral commonly known as table salt, rock salt or simply salt. Halite is composed of sodium and chlorine in equal proportions (NaCl). Rock salt and halite are not exactly synonymous terms. Halite is a mineral, rock salt is a type of rock that is predominantly composed of halite. Halite is an evaporite mineral. These are water-soluble minerals that crystallize out of concentrated aqueous solutions.

Halite with other salts on the shore of Mono Lake in California. Width of view approximately 50 cm.

Badwater Basin in Death Valley is the lowest point in North America. The floor of the basin is covered with halite.

Crystals of halite are cubic but that does not mean that they are cubes in shape. Their cleavage is cubic because of internal crystal structure, the angles between cleavage planes are 90 degrees but the crystals may be elongated. It simply depends on external forces that shattered the crystals into many rectangular blocks. Take a look at the first picture below which shows halite crystals with various shapes.

http://picasaweb.google.com/107509377372007544953/Rocks#5798776677524013842
Halite crystals demonstrating perfect cubic cleavage.

http://picasaweb.google.com/107509377372007544953/Rocks#5848243670328049762
Crystal of halite. Pure halite is colorless and translucent. Width of the sample is 5 cm.

Halite crystals covering a quay on the Atlantic coast in Morocco. These salt crystals formed when seawater evaporated.

Pure halite is a transparent mineral. Halite is pretty soft (2.5 on Mohs scale) and gets easily scratched. So in reality the crystals are mostly not perfectly transparent. Impurities give various shades of color to halite. Especially rock salt often has light orange, yellow, gray, or brown color. Blue and violet colors are caused by lattice imperfections. Such defects may result from exposure to radioactivity.

Halite is very easily soluble in water as we all know because this mineral has a salty taste. It would have no taste at all, if it were not soluble. The taste of halite is one of the basic tastes that out tongues easily detect. For some reason people love this taste. Most of us tend to consume much more salt than really needed (hundreds of times more than needed is not unusual because processed food is full of salt). One of the reasons we love salt may be the fact that it is not only salty, but salt also helps to enhance the flavor of food which is an important component of taste.

Crystals of halite are very brittle. You can easily make many small rectangular halite crystals from one big crystal. All it takes is just a light hammer blow. I have written an article which attempts to explain why halite and other ionic compounds are so brittle: What makes minerals brittle.

Solution of halite in water is essential for humans and other animals. Our nerves can not function without salt. Our cells would quickly swell because of osmosis and death would be inevitable without salt. That doesn’t mean that we should drink saltwater. Normal freshwater is adequate because it does contain salt from weathered rocks. Water flowing in rivers carries it to oceans which become more salty as time goes by because water escapes oceans by evaporation but salt does not. That does not mean that there is no mechanism to remove salt from oceans. Salt forms in shallow lagoons in hot areas but water has to have a really high concentration of salt for that.

Salt is an important industrial raw material. Halite is of course used in food but this is not the most important use nowadays. Salt is used as a principal source of chemical element chlorine. Chlorine gas and hydrochloric acid are the major products for which halite is a raw material. Halite is used in agriculture (fertilizer, weed killer, cattle feed stocks). Halite is extensively used as a road deicer in certain regions.

Salt should be really inexpensive and widely available if it is used to keep roads ice free. Indeed, this is the case. Many raw materials like metal ores and crude oil are non-renewable resources which no doubt become more and more expensive in the future but this is not the case with salt. We have more than enough of it for any need that may arise in the future. It is pretty safe to say that we will never run out of salt.

However, in the past, things were different. Salt used to be very expensive commodity and certain cities in southern Europe (especially Venice) became rich because of salt trade. Even the word “salary” (salario in the Italian, salarium in the Latin) comes from sal (salt). Venice (and even Roman Empire well before that) used to make lots of money by selling salt before people learned that you can get salt by simply evaporating sea water in ponds.

Nowadays salt is either mined, collected from evaporation ponds or pumped out from salt deposits. In order to do that, water is pumped into a salt deposit through a drill hole. This water dissolves the salt to form a brine which is pumped out. The brine is either used directly by an industrial plant or pumped to an evaporation pond.

http://picasaweb.google.com/107509377372007544953/Rocks#5798776692398641602
Evaporation pond in Israel. White material in the background is salt.

http://picasaweb.google.com/107509377372007544953/Rocks#5798776696077098210
The Dead Sea is a salt lake between Israel and Jordan. Its surface is more than 420 meters below sea level. You can not go lower than that on land but new record is set every year because the water level of the Dead Sea is constantly falling. The Dead Sea is hypersaline — every liter of water contains over 330 grams of salt, mostly dissolved halite. This is almost ten times more than in sea water. That increases the density of water (1.24 g/cm³) and makes drowning pretty much impossible. It is me on the picture above floating effortlessly in the water. Swimming in the Dead Sea is an interesting experience. I am used to cool lakes in northern Europe where swimming is really refreshing experience. The water in the Dead Sea was hot (although certainly cooler than the air temperature which was about 45 °C that day) and had a funny soapy feel. If I were living next to Dead Sea, I would not go swimming there regularly. It simply does not make any sense. It gives no relief from hot weather and when you have even a tiny skin scratch somewhere it surely does hurt while trying to swim there. The bottom of the Dead Sea near the shore is not covered with normal sand. It is salt. This is weird place indeed.
http://picasaweb.google.com/107509377372007544953/Rocks#5798776706728102082
The Dead Sea is shrinking because people consume the water of the River Jordan that should feed the lake. This is sad but so far no solution to the problem has been found. Former bottom of the Dead Sea is on the picture above. Now it is just a barren land covered with salt and mud. However, the Dead Sea, unlike the Aral Sea, is likely not destined to disappear entirely. At least not in the near future because the lake occupies a tectonic depression, the Jordan Rift Valley, which is basically an extension of the Red Sea. Because of that, the Dead Sea is deep (377 meters) and will make tourists (over one million every year) happy for many years to come.
http://picasaweb.google.com/107509377372007544953/Tenerife#5821093330984695138
Salt pans on La Palma, Canary Islands. Water in salt pans is often colored because of various extremophile microorganisms. Alga Dunaliella salina is one of the most common of them. Shrimps that also tolerate high salinity feed on it. Birds, for example flamingos, look for shrimps as a food source but not only food. Their beautiful pink wing coloration is a result of pigments (carotenoids) produced by these microorganisms that live in saline water.
http://picasaweb.google.com/107509377372007544953/Tenerife#5821093331599709378
Salt extracted from seawater on La Palma.

Variscite is a rare hydrated aluminum-bearing phosphate mineral (AlPO₄·2H₂O).

The mineral is usually pastel shade of green. It resembles turquoise but is usually greener (turquoise has more bluish tone). These two minerals are also chemically related (both are hydrated Al-bearing phosphates) and may occur together. Copper content is the principal difference between them. Copper is an essential constituent of turquoise, but it is absent in variscite. Both minerals are valued semi-precious stones.

Variscite occurs in host rocks as a cementing material filling cracks or in nodular form. Most important deposits are known from Utah and Nevada. It occurs also in Australia, Brazil, Germany, etc.

Variscite forms veins in shattered rocks, but it is not a hydrothermal mineral. It was groundwater that carried phosphatic material to the deposition place in contact with Al-rich rocks. Variscite precipitated out of water at near-surface temperatures. The source rocks were therefore located above from the site of precipitation, not below. Phosphatic groundwater is common in areas that contain phosphatic deposits (mostly sedimentary phosphorites). Aluminum is from silicate minerals.

http://picasaweb.google.com/107509377372007544953/Rocks#5793295613584912802
Filling the cavities in a brecciated fine-grained sandstone. Width of sample 11 cm. Queensland, Australia. TUG 1608-5222

Orpiment is an arsenic-bearing sulfide group mineral (As₂S₃). It is known as a yellow mineral although the color may vary between darker (brownish) and brighter tones.

http://picasaweb.google.com/107509377372007544953/Rocks#5791358209284023394
A sample from Zirneihbad, Kurdistan (Iran). Width of sample 9 cm. TUG 1608-1830.

The yellow color makes orpiment often similar to sulfur and these minerals may occur together in volcanically active areas, but orpiment has good cleavage (crystals are leafy) which may help to identify it if crystals are large enough to be seen. Orpiment is soft (Mohs hardness 1.5-2) and can be cut with a knife. Cleavage laminae are flexible but not elastic.

It came as a surprise to me that both Webmineral and Wikipedia claim that orpiment is a common mineral. I have hard time accepting that because orpiment contains arsenic which is not a common chemical element in the crust. Arsenic makes up only 1.8 ppm of the crust (which makes it less abundant than europium, for example) and orpiment is not the only mineral containing arsenic. Arsenic may occur in native form and realgar and arsenopyrite are well-known arsenic-bearing minerals as well. More than 100 minerals contain arsenic but most of them are exceedingly rare. Hence, I would say that orpiment as a common mineral seems to be an exaggeration. Whether it is rare depends on what is the definition of rareness.

What is the cause of such a confusion? I think the main reason is that it is a quite well-known mineral and has been pretty famous or maybe I should say infamous for a very long time. Golden yellow color of this mineral tricked alchemists to believe that it contains gold. Another reason to become famous is the fact that it is very toxic (because it contains arsenic). Inorganic arsenic is especially hazardous. It has been used to kill countless people. Orpiment (and other arsenic compounds) used to be very good poisons because it was difficult to say what exactly was the cause of death. Nowadays it is not the case anymore, arsenic poisoning is easy to detect. However, arsenic poisoning remains to be a major environmental and health-related concern. Drinking water is allowed to contain only up to 5 ppb or arsenic. Groundwater in many regions contains much more. It is estimated that well over 100 million people live in areas where groundwater contains too much arsenic to be considered safe to drink. Plants also pick up arsenic, but in organic compounds arsenic is not nearly as dangerous.

Orpiment is usually associated with realgar (AsS). These minerals precipitate out of volcanic gases or from hot springs and low temperature hydrothermal solutions.

The name “orpiment” is derived from Latin (auripigmentum) which means “golden paint”.

Crocidolite is a fibrous variety of riebeckite. Riebeckite is a silicate mineral belonging to the amphibole group. Usually I do not devote an entire post to just a variety of one mineral but in this case I believe we have a fairly good reason to pay more attention to it.

http://picasaweb.google.com/107509377372007544953/Coll#5779170714655278658
A sample of crocidolite from South Africa showing the fibrous nature of the mineral. Width of sample 3 cm.

Crocidolite is one of the asbestos minerals, it is also known as the blue asbestos. Blue color sets it apart from other asbestiform minerals. Crocidolite is a relatively rare mineral with very restricted occurrence, it is found in metamorphosed iron formations as slender and flexible fiber bundles.

The health risks associated with asbestos (sometimes misspelled abestos) are generally well known. A lot less known is the fact that asbestos is not a single mineral, not even a single mineral group. All asbestos minerals are fibrous. This defining property of all the asbestos minerals makes them potentially hazardous — inhaled asbestos fibers may damage the lungs and are known to cause serious diseases as asbestosis, lung cancer, and mesothelioma (a rare form of lung cancer mostly caused by the exposure to asbestos).

However, the nature of fibers of different asbestos minerals varies. By far the most widely used asbestos mineral is chrysotile which belongs to the serpentine mineral group. It is green in color and its fibers are actually microscopic rolled sheets (serpentine is a sheet silicate just like clay minerals and micas). The evidence that these rolled sheets cause aforementioned diseases, especially mesothelioma, is less convincing as is the case with amphiboles: “For mesothelioma, the hypothesis that chrysotile and amphibole asbestos are equally potent (rpc = 1) was strongly rejected by every metric and the hypothesis that (pure) chrysotile is nonpotent for mesothelioma was not rejected by any metric”¹.

It is even more important to understand that a low-level exposure or even a single high-level exposure to asbestos, no matter what type, is very unlikely to cause a serious disease. It takes a long-term exposure to fibers to cause harm. I would be concerned if I were a miner or a construction worker but otherwise I can not find a justification for wasting enormous amount of money to replace construction materials which are in many cases somewhat difficult to breathe in.

But what about crocidolite? What makes it different and do we have a reason to be concerned? First of all, there is a fundamental structural difference between a sheet silicate serpentine and a chain silicate amphibole. Amphiboles are composed of many slender and often sharp chains which seem to cause much more harm to human lungs. There are many different amphibole minerals which have fibrous varieties but crocidolite seems to be among the most hazardous of them.

Ironically, it often happens that inventions which are at least partly meant to protect our health do just the opposite. Remember margarine which was long believed to be less harmful to our health than butter which is rich in saturated fats. Only recently we discovered that hydrogenated vegetable fats are actually much worse. Something similar happened with crocidolite as well. Cigarette filters where invented to reduce the amount of tar and particulate material inhaled by smokers. However, such filters do more harm than good if crocidolite is used in their composition. This was the case with Kent’s Micronite filters from 1952 to 1956. It only makes me wonder what are the killers of today which we are used to think as our protectors. There are definitely many.

References

1. Berman, D.W. & Crump, K. S. (2008). A Meta-Analysis of Asbestos-Related Cancer Risk That Addresses Fiber Size and Mineral Type Critical Reviews in Toxicology DOI: 10.1080/10408440802273156