Monday, June 8, 2009

Obsidian Notes

Today is partly a workshop day - I have 120 small fibre optic points to notch for the three outstanding wholesale orders I have left to fill. I spent all week last week getting the blanks to this stage, so I'll be happy when they are finally finished.

This afternoon I need to do a little prep work for a flintknapping demonstration in Portugal Cove this evening. Its for 31 Beavers and Cubs who are learning about archaeology. That's a fun age and there are always lots of questions which keeps the demo interesting for me.

In a demonstration like this with a beginning, middle, and end I use obsidian. I know that I can go from a rough core to a finished point without any bad surprises along the way. The obsidian that I use comes from Oregon, so its not exactly local. I've been told by geologists that there would have been obsidian in Newfoundland in the past, but that it devitrified long ago. Over tens of millions of years quartz crystals grow in the obsidian and eventually the stone loses all of its glassy properties, that's what is meant by devitrification. One popular kind of obsidian that you can often find in pet stores for fish tanks is called "snowflake" obsidian. The white snowflake crystals (called cristobalite) growing in the rocks are devitrification in action. Flintknappers avoid this kind of obsidian because those crystals are tough and unpredictable to knap through. In Newfoundland, the closest relatives we have to obsidian are rhyolite and granite - which have the same mineral make-up, but which cooled from molten rock more slowly and under different temperatures and pressures. I'm sure I'll talk more about rhyolite in the near future.

Obsidian is natural volcanic glass that forms when lava cools so quickly that it doesn't develop a crystal structure. Which is why its so good for knapping -- it has no grain and is completely homogeneous throughout. Its primarily silica, and different minerals in the lava flow will produce different colours; magnesium and iron give us black and red. Theoretically, when you chip obsidian the edge of the flake will feather out to one molecule thick. This creates an extremely sharp edge, but also an extremely fragile edge. Don Crabtree, the flintknapper who taught my flintknapping teacher, had heart problems and insisted that his heart surgeons use obsidian scalpels of his own making during his surgeries. They were very sharp and Don's scars healed quickly, although the scars were itchy and occasionally tiny glass shards would pop out when he scratched. Obsidian scalpels are still kept on hand at many hospitals - I've been told that they are used at the Health Science's Centre in St. John's for people who have metal allergies.

Photo Credits:
Top, Lori White
Middle, Rockhound Blog
Bottom, Tim Rast

Photo Captions:
Top, Tim about to remove a large flake from an obsidian core using a hammerstone
Middle, Snowflake Obsidian
Bottom, Two obsidian knives ready to be hafted. The obsidian in the top, red knife may be a little older than the black one, because it is peppered with tiny cristobalite snowflakes.


  1. That Heart surgery story is AMAZING! I never in a million years would have thought a surgeon would agree to that, and had no idea flint scalpels were still actually sometimes still used for surgery. Very Interesting! Your blog is terrific!

  2. Thanks Paul, here's an article you might find interesting, its called "Ancient Technology in Contemporary Surgery" and was written by a physician who did some medical experiments with Crabtree's obsidian scalpels:

    I'll be honest, some of the experiment descriptions might make young or sensitive readers queasy.


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