Obsidian is formed when rapidly cooling ions are randomly distributed creating a texture
a. glassy
b. fine-grained
c. course-grained
d. porphyritic

Obsidian is formed when rapidly cooling ions are randomly distributed creating a a. glassy texture.

Obsidian is a type of mineraloid, which is formed when liquid content of the volcanic material cools so quickly that particle lacks ability to transform into a crystalline structure. The outcome is a volcanic glass with a smooth uniform surface that breaks with a conchoidal crack.  

As a “glass”, obsidian is artificially shaky. With the progression of time, some obsidian starts to solidify. This procedure doesn't occur at a uniform rate all through the stone. Rather it starts at different areas inside the stone. In these areas, the crystallization procedure structures spiral groups of white or dim cristobalite gems inside the obsidian. Whenever cut and cleaned, these examples are alluded to as “snowflake obsidian”.