Volcanic Glass – Obsidian

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.

Lava eruption

Lava eruption (www.bhargavaz.net/rashi/volcano.html)

This is the Newberry Volcanic Monument in Oregon, USA.  Check out the solidified lava flow (obsidian glass) near the lakes.

Lakes and Lava Flow, Oregon USA. Photo:QTLuong

Lakes and Lava Flow, Oregon USA. Photo:QTLuong (www.terragalleria.com)

Pond at the edge of the lava flow.  Photo: QTLuong

Pond at the edge of the lava flow. Photo: QTLuong (www.terragalleria.com)

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.

Obsidian Flow (black).  Photo: janined

Obsidian Flow (black). Photo: janined (www.flickr.com/people/janined/)

Mahogany Obsidian.  Photo:MineralData

Mahogany Obsidian. Photo:MineralData http://www.mindat.org/min-27030.html

"Snowflake" Obsidian.  Photo

"Snowflake" Obsidian. Photo: GreatCabochons.com/cabs57.shtml

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.

Conchoidal Fracture. Photo:Geology.com

Conchoidal Fracture. Photo:Geology.com http://www.geology.com/rocks/igneous-rocks.shtml

Conchoidal Fracture

Conchoidal Fracture http://www.geology.about.com/ Click picture to link

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.

Obsidian Flint Chips.  Photo: Andrew Alden

Obsidian Flint Chips. Photo: Andrew Alden (click picture to link)

Sharp edges that are "flint knapped".

Sharp edges that are "flint knapped". http://www.obsidianlab.com/terminology.html

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?

Banded Obsidian.  Razor sharp.

Banded Obsidian. Razor sharp. http://www.gc.maricopa.edu/ (Click picture to link)


4 thoughts on “Volcanic Glass – Obsidian

  1. RaiulBaztepo says:

    Very Interesting post! Thank you for such interesting resource!
    PS: Sorry for my bad english, I’v just started to learn this language 😉
    See you!
    Your, Raiul Baztepo

  2. PiterKokoniz says:

    Hello !! ^_^
    My name is Piter Kokoniz. Just want to tell, that I like your blog very much!
    And want to ask you: what was the reasson for you to start this blog?
    Sorry for my bad english:)
    Thank you:)
    Your Piter Kokoniz, from Latvia

  3. mostafa says:

    very very nice stuff

  4. Mary says:

    some people found a little piece of black obsidian in a lake , in my country (Moldova), but there is no volcano.how it’s explaning?

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