Obsidian

Definition: Obsidian is a natural volcanic glass formed from the rapid cooling of felsic (silica-rich) lava. It lacks a crystalline structure because it cooled too quickly for crystals to form. Composition: Similar to rhyolite or granite (70-75% silica), but in glass form rather than crystalline. Color: Usually black, but can be: - Brown - Red - Green - Gray - Sometimes banded or with inclusions Texture: Glassy, smooth. No visible crystals.

How It Forms: Obsidian forms when felsic lava cools extremely rapidly: - Lava flows cool quickly at surface - No time for crystals to form - Results in glass rather than crystalline rock Where It's Found: - Volcanic areas with felsic eruptions - Lava flows - Volcanic domes - Areas with recent volcanic activity Geological Settings: - Rhyolitic volcanic areas - Areas with viscous, silica-rich lava - Often associated with pumice

Hardness: 5-5.5 on Mohs scale (relatively soft for a glass) Fracture: Conchoidal (curved, shell-like). Creates very sharp edges. Luster: Vitreous (glassy) Transparency: Opaque in thick pieces, translucent in thin pieces. Uses: - Tools and weapons (historical and modern) - Decorative objects - Jewelry - Surgical blades (extremely sharp edges)

Black Obsidian: Most common variety, pure black. Mahogany Obsidian: Brown and black banded. Snowflake Obsidian: Black with white cristobalite inclusions (snowflake pattern). Rainbow Obsidian: Shows iridescent colors when polished. Apache Tears: Small, rounded pieces of obsidian. Sheen Obsidian: Has a golden or silver sheen.

Collecting Considerations: - Beautiful glassy appearance - Sharp, interesting fracture patterns - Historical significance (used for tools) - Some varieties are very attractive Where to Look: - Volcanic areas - Lava flows - Areas with recent rhyolitic eruptions - Known obsidian sources What to Collect: - Pieces showing conchoidal fracture - Colorful varieties - Snowflake obsidian - Rainbow obsidian - Large, clear pieces