Snowflake Obsidian 8x10-9x13mm Side Drilled Pebble - 15-16 Inch Calcite Petrification occurs when the wood

Petrification occurs when the wood is covered by sedimentary rock

The image shown has 3 cabochons to give you an idea of the range possibilites of the colors

including browns

sometimes with a striking black or brown matrix therefore giving it a more traditional look with blue dominance

The most common colour of aventurine is green

Snowflake Obsidian 8x10-9x13mm Side Drilled Pebble - 15-16 Inch Calcite Petrification occurs when the woodSnowflake Obsidian is a volcanic black stone with small, white, radially clustered inclusions of cristobalite in the black glass, producing snowflake patterns. Obsidian is formed when felsic lava cools without crystal growth. It is sometimes used for scalpel blades in cardiac surgery, as Obsidian can be formed into a blade many times sharper than steel surgical blades.