Obsidian is a naturally occurring non-crystalline solid. It forms from lava which cools relatively quickly hence crystals do not have time to grow.
Colours and markings in obsidian are dependant on the impurities present. In this variety the deep reddish brown colour is caused by iron oxides mostly likely from hematite. One of the most common iron oxides is rust.
This mahogany obsidian pendant has been mounted in a fine sterling silver setting. It has been slightly reduced because of some minor damage to the back of the stone.