In the late 1980’s I had a geology lecturer named George whose humour was as dry as the rocks we were studying. His lessons were always interesting and I clearly remember crates of rocks and minerals, assorted hammers (for all occasions) and lots and lots of dust. It was during his class that I learned about igneous rocks and handled some incredible volcanic glass.
Obsidian is volcanic glass that is molten lava one minute and solid the next.
This is the Newberry Volcanic Monument in Oregon, USA. Check out the solidified lava flow (obsidian glass) near the lakes.
The lava cools so quickly it doesn’t form crystals like other igneous rocks (think Granite). Instead, it cools rapidly and forms globules of glass that look deceptively like a sweet jelly. It is often black, but depending on the minerals near the lava flow it can be coloured, or have ‘bands’ running through it.
When obsidian breaks, it doesn’t snap or cleave in clean lines like other rocks or minerals. It breaks in a circular, concave or convex curves. This is known as “conchoidal fracture” and gets its name from the latin word for seashell, because of the spiral like pattern.
It’s easy to imagine ancient civilisations using obsidian as tools and cutting blades. It is durable, micro thin and extremely sharp. The Egyptians used obsidian scalpels during their surgery and embalming rituals.
It’s interesting to note that for surgical procedures today that require fine incisions (think cardiac surgery), our surgeons are returning to precision obsidian scalpels rather than the much ‘thicker’ steel blades. Amazing huh?