I am happy to announce that I will soon leave home to discover new and interesting places. I have never been that far from home. I plan to visit two world-class geological destinations: Big Island of Hawaii and Death Valley in USA. I will go in the second half of this month and the whole trip will last about one month.
I will spend most of the time in Hawaii and about 10 days in southern California on the way back. This is not much. I know that California has interesting hiking trails and outcrops for more than a lifetime of travels. However, I have to try to take the best out of these days. I am sure some of you live in California or have been there and can recommend places worth visiting. I will arrive to Los Angeles and plan to rent a car to go to Death Valley and visit geologically interesting places along the way. I have no idea at the moment which places these are. You can help me to make the best selection.
I will try to make my best to take you along by posting pictures of interesting geology I will see there. I am really looking forward to this trip.
Conchoidal fracture is a smoothly curving fracture surface of fine-grained materials which have no planar surfaces of internal weakness or planes of separation (no cleavage). Such a curving fracture surface is characteristic of glass and other brittle materials with no crystal structure. However, conchoidal fracture is common in crystalline materials also if they have no cleavage (like mineral quartz), or if they are composed of very small mineral grains so that the fracture surface which is actually zigzagging between the grains appears smooth to our eyes. This is the case with many fine-grained (aphanitic) rocks.
http://picasaweb.google.com/107509377372007544953/Rocks#5848238745712314674 Obsidian is famous for its conchoidal fracture surface. This rock type was highly valued during the Stone Age because it makes a fine cutting blade if treated (fractured by precise and forceful blows) correctly. Width of sample is 11 cm.
Smoothly curving fracture surface develops when force is rapidly applied to brittle objects like hitting a piece of obsidian (volcanic glass) with a hard pointy object. If the force is applied correctly, a flake of obsidian is peeled away leaving obsidian with a smoothly curving fracture surface and sharp edges. It was the way our ancestors made sharp cutting tools.
Why is the fracture surface smoothly curving? Because we apply a force to only one point. This is where the brittle deformation starts. The energy of the blow spreads in the material like seismic waves travels through the Earth. So the curving lines are like the fronts of seismic energy recorded on the fracture surface. The fracture can occur only if the blow is energetic enough to peel off a flake. We need to apply more force if we want to shatter a large piece of material and much less if we just want to peel off a small flake from the edge.
http://picasaweb.google.com/107509377372007544953/Rocks#5848481665432908098 Another piece of obsidian with nicely curving conchoidal fracture surfaces. Width of sample from Armenia is 11 cm.
http://picasaweb.google.com/107509377372007544953/Rocks#5791275565177698226 This rock sample looks very much like obsidian but it is actually an amorphous fine-grained asphalt known as gilsonite. It has no crystalline structure and it is brittle at room temperature when force is applied rapidly. The sample from Mexico is 11 cm in width.
Even crystalline rocks like basalt may display conchoidal fracture if they are fine-grained enough. However, the fracture surface is not as smooth and shiny because microscopically it is pretty rough. Width of the sample is 12 cm.
http://picasaweb.google.com/107509377372007544953/Chert#5785454442189877602 Chert is another rock type that commonly exhibits a conchoidal fracture. It was also widely used as a tool-making material by our ancestors. Width of sample from Cyprus 7 cm.
http://picasaweb.google.com/107509377372007544953/Rocks#5842989770630082594 Quartz is a mineral with crystalline structure, but there are no planes of weakness inside the crystal. Hence, it has no preferred planar surfaces along which to break. Quartz is not the only mineral without cleavage, but it is the best known and most widespread of them. Smoky quartz on the picture. Width of sample 11 cm.
http://picasaweb.google.com/107509377372007544953/Rocks#5851584483551973970 Chalcedony is a very fine-grained rock type that is compositionally close to quartz and chert. There is a red variety of chalcedony which is known as carnelian on the picture above. Red color is given by hematite impurities. The sample from Kazakhstan is 14 cm in width.
“Conchoidal fracture” is named so because the curved lines on the fracture surface resemble the rippling growth lines on the shells of clams or conchs. The sample above is sandstone with abundant phosphatic brachiopod (Lingulata) shells from the Ordovician of Estonia. Brachiopods look similar to clams. Their shells have similar growth ripples. Pay attention to the fact that conchoidal fracture only looks similar to the appearance of clam shells. Their origin is completely different. Width of sample is 12 cm.
Today is a birthday. Not my birthday but my dear home country Estonia is 95 years old now. I wish her a prosperous future. May it be much brighter than the past.
Estonia’s national colors are blue, black and white and this post is inspired by these colors.
http://picasaweb.google.com/107509377372007544953/Rocks#5848481675389848706 This is a sample of hematite. Hematite is an oxide of iron. It is extremely widespread mineral, especially in sedimentary rocks. Many reddish rocks and minerals owe their color to hematite. Ironically, there is nothing red in this picture of a pure sample of hematite but it would be red if powdered.
The colors that dominate on the picture above are dark brown with white and bluish spots — the approximate colors of the national flag of Estonia. Dark brown is the natural color of hematite, white spots are reflections from the light source but what about the blue spots?
I have to say that I am really not sure. Some minerals possess a very beautiful play of colors called iridescence. Especially well-known example is a plagioclase feldspar mineral labradorite:
Plagioclase crystals in this sample of anorthosite look bluish when viewed from a certain angle. Plagioclase crystals allow some light to penetrate into the crystal which is made of many alternating slabs of different composition which act like mirrors and reflect the light back. Reflected lightwaves combine (this is called interference) and create interesting bluish play of colors.
Is the same effect responsible for the bluish spots on hematite? No, I don’t think so because hematite is practically opaque mineral which does not allow light to penetrate into it. But is it still caused by some intrinsic property that is specific to hematite?
This is also not likely. I have seen very similar effect in other minerals and rocks and I even remember some comic books which I read when I was much younger. It was about Native Americans that always had pitch black shiny hair with bluish glare. I doubt that they really have hair like that but maybe some tribes with very dark hair in some conditions? Somehow artists had to get the idea.
http://picasaweb.google.com/107509377372007544953/Rocks#5847099160896443730 Smoky quartz is a silicate mineral that also reflects bluish light.
http://picasaweb.google.com/107509377372007544953/Rocks#5848481665432908098 Obsidian is a glassy volcanic rock with occasional bluish reflections.
Smoky quartz is a silicate mineral, obsidian is a volcanic glass, and hematite is an oxide of iron. They are all very different materials. We can therefore almost certainly rule out the possibility that the bluish color has anything to do with the internal structure of these materials.
However, the surfaces of these samples have something in common — they all reflect light well and they are very dark-colored, almost black.
This in probably the key to understand this phenomenon. Blue color may be a weak reflection which looks bluish because it comes from a very dark surface. This is my guess. I have not found any confirmation to this. I would be interested to hear your opinions if you have an alternative explanation.
Do you know what causes these speckles in a mafic lava rock? These rock samples are from La Palma (Canary Islands) and appear to be basanite or olivine-phyric basalt. This is no quiz question. I don’t know the answer but hopefully someone with more experience has seen such rocks before.
http://picasaweb.google.com/107509377372007544953/Tenerife#5837857393000066994 Width of sample approximately 30 cm.
http://picasaweb.google.com/107509377372007544953/Tenerife#5837857399900679986 Width of sample 8 cm.
I am now back home in Estonia. I am very satisfied with my trip to Tenerife. It was not purely geological trip. We (I was there with my wife) also visited zoo, took a sea trip to spot dolphins and spent a whole day in a water park.
I have visited three islands in the Canary archipelago now and can say that they are all quite different. Gran Canaria is more eroded and noticeably older. La Palma looks and is very young with abundant examples of fresh volcanism but Tenerife is the most versatile. If I have to pick one which is the best of the three then I would be in trouble.
La Palma and Tenerife are both very interesting. I don’t know which one is the best. I probably have to go there again and take another look 🙂 Gran Canaria is probably somewhat behind the two but I also spent less time there.
Don’t hesitate to contact me if you plan to go to Tenerife to enjoy geology. I have many nice locations with coordinates recorded in my field notebook.
http://picasaweb.google.com/107509377372007544953/Tenerife#5834503856326911906 Tenerife Lizards or Western Canaries Lizards (Gallotia galloti) are common reptiles in Tenerife. I saw them in several places. They are usually very quick but this female lizard agreed to pose for a photo.
Today I took a very scenic hike in the NW part of Tenerife. This part of Tenerife is geologically known as Teno. It is one of the three original basaltic islands that were later joined into one bigger island.
I was hiking about 800 meters down along the Barranco de Masca and later up again. It took a little less than 6 hours and was physically quite demanding. This barranco is a deep and very narrow canyon. Maybe 200 meters deep in the lower part and 60 meters wide. I do not know the exact numbers at the moment. This is just a guess.
Volcanic islands are cut by lots of dikes that once fed the volcanoes higher up. They are easily noticeable in a vertical wall of canyon. Today I am showing you one which I took just before entering the canyon. Most of the photos I took later are unfortunately not that good because I did not want to hike with a tripod but there was not enough light at the bottom of the canyon to take good handheld shots.
http://picasaweb.google.com/107509377372007544953/Tenerife#5833805433454016130 This dike stands out as dikes often do because they tend to be more resistant to weathering than the surrounding volcanic material.
I am in Tenerife. Today was very long day in the field. I am too tired to write a lengthy post. But I would like to share at least one picture with you.
http://picasaweb.google.com/107509377372007544953/Tenerife#5832686321337998642 This is pyroclastic sequence which is composed of dark layers of scoria and light-colored layer of phonolitic pumice fall deposit between them. Pumice layer is a product of violent plinian eruption farther away. Scoriaceous mafic dark-colored lapilli were ejected from nearby vents (strombolian eruptions). You can also see a minor fault running through the outcrop.
Here are the coordinates of the outcrop: 28° 20′ 02″ N 16° 27′ 50″ W. Altitude 1970 meters.
One month ago I came from the Canary Islands (La Palma and Gran Canaria). Now I am going there again. But this time my destination is Tenerife.
I have been in Tenerife once (in 2009). It was a memorable trip. I know several nice outcrops there but this time I hope to see and understand much more. I just took a review of my photos I took there. I am really amazed how poor is the quality of these snapshots. There is really nothing I would like to use here now. Tenerife is a beautiful and magnificent island (second largest island volcano in the world after Hawaii). It deserves better equipment than my point-and-shoot I used then and better photographer also. I have a better camera and lens now but I am not sure about the photographer. It is still only me.
This time my trip will be quite civilized. I will stay at a hotel. Who knows, maybe I will even have internet access there. I am not very optimistic though. People there have somewhat different lifestyle. It seems that internet is not a necessity for them. Sometimes they advertise that their hotel has internet access but in reality this means that there is a computer in the lobby into which you can insert a coin to access internet for 5 minutes. It would be laughable if it were not so sad.
If there is internet access, then I will try to post something once in a while.
http://picasaweb.google.com/107509377372007544953/Tenerife#5831557066402030482 I took this photo a month ago when I was flying from La Palma to Gran Canaria (Tenerife is right between these islands). Quality of the photo is terrible because it was taken with a phone but phonolitic cone of Mount Teide, the highest peak of Tenerife (3718 meters) and the rim of the caldera surrounding it are clearly recognizable.
Rock fences are interesting to take a look at. They usually reflect local geology remarkably well because it is expensive to transport such a heavy material which is readily available in most places. Here I present a collection of images of rock fences and walls I have taken so far.
Unfortunately my collection is very small but this post in its current state is just a start. I plan to update it as I take new photos. Now I have a reason to hunt these walls and a place where to upload the photos.
http://picasaweb.google.com/107509377372007544953/Syenite#5830113426498557362 Ignimbrite (welded tuff). Gran Canaria, Canary Islands, Spain.
http://picasaweb.google.com/107509377372007544953/Syenite#5830113424034192210 Mudstone (turbidite). Cliffs of Moher, Ireland.
http://picasaweb.google.com/107509377372007544953/Syenite#5830113420524292018 Andesite or basaltic andesite. Red blocks are weathered. Santorini, Greece.
http://picasaweb.google.com/107509377372007544953/Syenite#5830113476261131490 Quartzite. Connemara, Ireland.
http://picasaweb.google.com/107509377372007544953/Syenite#5830113517544186034 Basalt or basanite. La Palma, Canary Islands, Spain.
Tuff (ignimbrite). Gran Canaria, Canary Islands, Spain.
http://picasaweb.google.com/107509377372007544953/Syenite#5830113478740527506 Quartzite. Santorini, Greece.
http://picasaweb.google.com/107509377372007544953/Tenerife#5835287153442706386 Ignimbrite. Tenerife, Canary Islands, Spain.
http://picasaweb.google.com/107509377372007544953/Tenerife#5835533261787961666 These rocks may look like man-made bricks but they have entirely natural composition. This is the same Tenerife ignimbrite shown in the previous picture.
http://picasaweb.google.com/107509377372007544953/Tenerife#5835482892065455538 Pumiceous lapillistone (pumice fall deposit known as Granadilla pumice), Tenerife, Canary Islands, Spain.
http://picasaweb.google.com/107509377372007544953/2015#6191004866314945746 Wall made of gneiss in Sweden.
This post is political. There is no geology. Stop reading if you are not interested in it.
I know I should not care because it will not change anything but sometimes I feel that now my limit to accept stupidity has been reached and I simply have to say something.
I do not know who made it and I do not care. I just don’t want to know. These people have nothing to tell me.
But I want to say few words about it as a non-American who is a free man now but was not when I was born. I want to say why people who produce such a crap are so badly mistaken.
I was born in Soviet Union but I am not a Russian. This evil empire was a prison of many nations with unfortunate histories. My home country is Estonia and it did not exist on the world map at that time. Not as an independent country since WWII. It was occupied by criminals who murdered and mass deported my people to Siberia. These criminals feared one thing above all — America. They invested so heavily into their military that eventually this country collapsed. It just could not keep the pace with America because their economy was deeply rotten and fundamentally flawed.
This world is full of seriously mad people. It happens so often that people who should be isolated in psychiatric hospitals are actually leading entire nations. Sometimes even empires. Stalin, for example. He was a terrorist and murderer. But he was not the only one. Hitler, Pol Pot, Hussein, etc.
As long as USA keeps attempting government overthrows, bombing, and sabotaging these criminals. So long I feel this world still has hope. Lots of people hate USA because they see it as a world policeman (ha, why are these people hating police anyway. I guess they have a reason like all criminals do). I love USA for this very reason. My own home country is probably free only as long as USA is standing behind our back. There is only one million Estonians. No matter how hard we try, we can not fight long against an enemy hundred times bigger without help from the free world. So far only USA seems to care and has will and resources to do that. Millions of people all over the world hope that USA has resources enough in the future to successfully deter and fight against mass murderers. I am sometimes ashamed to be a European because of that. We were not able to stop Slobodan Milosevic in 1999 in Kosovo on our own although it is our backyard. We had to ask help from Americans. We Europeans are like a bunch of 99 year old people. USA must come here regularly and change our diapers. It is a disgrace.
I am not so sure it will continue forever. I know that freedom is fragile and we all should work hard to keep it. Unfortunately, sometimes I see that some idiots among ourselves are producing pictures like the one above and I feel that I want to cry. Do they really think that leaders like Kim Jong-un and Mahmoud Ahmadinejad who both fear and hate USA are great humanists? You may say that they are no mass murderers either and perhaps you are even right but only because they lack resources to do that. Ahmadinejad would gladly wipe Israel off the map but his weak country has neither strength nor brainpower to do that. Kim would gladly welcome 40 million more Koreans in his huge labor camp if he only could do that. They can not at least partly because South Korea and Israel are supported by USA. I really don’t understand what is the compensation USA receives for providing protection to so many people all over the world.
I do not want to say that everything America does is right and they deserve no criticism. But this criticism should not be idiotic. Look at that list above. In my opinion Americans have every reason to be proud of it.
Anyway, I just want to express my sincere thanks for that.
