Past blog hops and challenges

Thursday, April 17, 2014

It's the letter "O" in the Blogging A - Z Challenge

Today’s topic starts with the letter “O”.
It was hard to decide which “stone” to pick for the letter “O”.  My choices were a volcanic glass, a mineraloid, and a banded variety of chalcedony. 
Since I had already blogged about chalcedony and didn’t want to blog about a mineraloid, I decided to go with the volcanic glass “stone” called obsidian.  It is formed when lava cools rapidly with little crystal growth.  It is commonly found in lava flows known as obsidian flows.

It is hard and brittle which breaks with very sharp edges.  Those edges have been used in the past as cutting and piercing tools. 
Pure obsidian is usually dark in color though the colors varies based on what impurities are in it.  Iron and magnesium usually give a dark brown to black color.  Some stones have an inclusion of small white, radially clustered crystals of cristobalite producing a blotchy or snowflake pattern thus snowflake obsidian. 

Snowflake obsidian

Obsidian can be found on most continents where there have been volcanic eruptions.  There are several areas in the US where you can hike on obsidian flows such as Medicine Lake Volcano in the Cascades, Inyo Craters in eastern California, and in Yellowstone National Park. 
Obsidian was valued in the Stone Age because like flint it can be broken to make sharp blades or arrowheads.  It was also polished to create early mirrors.
Thanks for stopping by and be sure to come back tomorrow to see what the letter "P" will be.

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