Obsequious Obsidian

Was missing a bit of obsidian for the little book, and Vangelis scanned me a piece. Obsidian with stripes (as this piece) shows the flow of the glassy material (like Venetian glass). The conchoidal fracture is due to the fact that there is no mineral structure, this is a "mineraloid" after all. Every archeologist in Greece has brought me little bits of black shiny artefacts hoping they are obsidian: apparently the stone age Greeks made knives and arrow points from obsidian from Milos Island (where there's a volcano), and to find an artefact of obsidian shows something about ancient trade. However, none of their little bits proved to be obsidian, most little bits of black chert of even serpentine. To see it, is to know it.

Sulphides in coal...

What geologist would be disappointed if Santa Claus left them a stocking full of coal -- if the coal was all full of pretty pyrite?
Yes, Virginia, pyritite is not only caused by hydrothermal processes, but also grows in reducing conditions such as this coal seam. Except as a "pretty rock" I don't think it's ever been mined in its own right for anything of economic use.
This lump of coal is about... 6 cm across. The pyrite is pervasive throughout.

Synthetic ruby

Only posting this because its glow and brillance on scanning surprised me. The ring is probably from the 1920's, and has been mine for about 50 years. I never suspected that it had such a glowing soul. A Christmas gift from my mom, oh, so many years ago.

Lava from Santorini

Once upon a time, there was a large island in the middle of the Aegean. Then it exploded, creating earthquakes, tsunamis, and a large hole in the middle of the sea. Civilizations were destroyed, myths born. And this, this lava!-- this is the culprit! Note all the holes from bubbles of volatile gasses that were the cause of the violent eruption.
Bad lava! Bad, bad!

Unakite is...

Essentially, it's a term that describes an altered granite that consists mainly of epidosite matrix and large pink orthoclase. I don't think it has any strict scientific meaning. However, it s a stone for collectors that is "pretty when polished up." Said to be found in Oregon and the Appalachiens, it seems to me a common enough rock within Pelagonia over here. Found in the oldest of the old parts of the metamorphic terrain. I just don't know if anyone in Greece has bothered to pretty it up. Maybe we should.
Scale on this slab cut from Dina's cobble: each orthoclase is on the order of 2 - 3 cm.