how to facet
gemstone main cabochon creation
min data

Mineral: obsidian (volcanic glass)
Gem: mahogany obsidian
Size: 32mm x 40mm
Carat: 48.6 ct
Cut: cabochon
Origin: unknown
General Info: Obsidian is rapidly cooled (high silica) glass formed in igneous volcanoes. It is usually black and has no crystal structure. The word obsidian may come from the Greek “Opsianos”, meaning vision. It was once used to make mirrors. Or it may be named from the person "Obsius" who was thought to have found a similar stone in ancient times.
Additional Information
This stone is called mahogany obsidian due to the brown swirl patterns trapped within. It makes the stone appear somewhat wood-like. Stone cut by author.

The color layers in obsidian are due to mineral fragments that were oriented to the flow patterns while the obsidian was still flowing. Other types of obsidian have may have trapped water oriented to flow patterns or small air bubbles. There are many varieties with a multitude of names: sheen, rainbow, and velvet are well known.

Snowflake obsidian is the result of a process called "devitrification". Obsidian is not stable as it is a glass, and the silica will slowly crystallize from the glass to form a secondary material, the process produces the white silica mineral that creates the snowflake pattern.

The image below is a sample of rainbow obsidian with a light directed into the center. It is roughly actual size.