Obsidian

Obsidian is a form of volcanic glass, it has been used as glass by ancient cultures.  Some call it smoky tears or Apache Tears, as it is said to resemble a tear when held up to the light. 

Snowflake obsidian is a solid black stone, often it will have white or grey "snowflakes" cover the black stone. Mahogany obsidian is very similar in appearance to snowflake obsidian, the difference is that in mahogany obsidian the spots are brown instead of white or grey. Gemstone cutters will spend time selecting and looking at the rock before cutting to choose the most interesting patterns for the making of jewellery. 

Obsidian is said to reduce stress and dispel negativity when worn. Some believe it may be effective in improving blood flow and in pain management.