Remnants of bottle messages

Trash thrown into the sea is a global and unfortunately ever increasing problem. Most of the garbage is plastic because the decay of this material takes enormous time. Another type of resistant trash dumped into the sea is glass.

A very small part of it may indeed come from castaway sailors sending bottle messages, but mostly it is the result of people using sea as a huge garbage dump. Glass is not as visible and annoying in the sea as plastic, because it is heavier than water and sinks to the bottom. And rounded glass pebbles can easily be mistaken for some minerals. Especially if the glass is transparent, it may look very similar to quartz.

In our particular case the transparent grains are indeed glass pebbles, not quartz. It is easy to distinguish between the two with the help of a polarizing microscope. Unlike quartz, glass has no crystal structure and is therefore dark (showing no interference colors) when placed between the two crossed polarizers of the microscope.

Sea glass has lost its sharp edges because of the tumbling action of waves. It is frequently washed ashore but the concentration of seaglass in the beach sand is usually very low. There are some notable exceptions such as the Glass Beach in Kauai Island or the Glass Beach of Fort Bragg in California. Glass has concentrated there because these places were used as a garbage dumps in the past.

Here are pictures of the sand samples from these locations. Although I am somewhat reluctant to say so, but I think we have to admit that even trash can sometimes become something beautiful.

Glass Beach, Kauai, Hawaii Islands. Transparent, green, and brown glass pebbles. Dark grains are fragments of olivine basalt (without olivine though which is due to weathering replaced by iddingsite). There are also biogenic grains (forams, mollusks, echinoids, and corals). The width of the view is 20 mm.

Glass Beach, Fort Bragg, California. Transparent, blue, and green glass pebbles. There are some biogenic grains (mollusk shells, echinoids) and rock fragments (mostly lithic sandstone). The width of the view is 28 mm.