Obsidian

Hardness: 5-6 on Mohs scale; Color: Typically dark, commonly black, but can be dark brown, green, or rarely red or blue; Luster: Vitreous (glassy); Crystal structure: Amorphous (no crystal structure); Cleavage: None, exhibits conchoidal fracture; Specific Gravity: 2.3-2.6

Formation process: Formed from rapidly cooling felsic lava (high in silica) that solidifies before significant crystal growth can occur, resulting in natural glass. Geological age: Primarily Cenozoic to recent, as it weathers relatively quickly over geological time, but can be found in older volcanic deposits.

Uses: Historically, it was used for making sharp tools, weapons, and ceremonial objects due to its extremely sharp edges. Currently, it is used for surgical scalpel blades, in jewelry as polished stones, and as decorative aggregate in landscaping.

Interesting facts: It is technically not a mineral because it lacks a crystalline structure. Some obsidian contains small, light-colored, radially clustered crystals of cristobalite, which resemble snowflakes, hence the name 'snowflake obsidian'. Apache Tears are small, rounded nodules of obsidian.

How to identify in the field: Look for its characteristic glassy luster and conchoidal (shell-like) fracture pattern. It will feel sharp to the touch along broken edges. Common locations: Found in areas of recent volcanic activity, such as Italy, Greece, Turkey, Mexico, Ecuador, Iceland, Japan, and the western United States (e.g., Oregon, California, Idaho, Wyoming). Tips for collectors: Be careful when handling broken obsidian as it can be extremely sharp. It often weathers into hydrated perlite over time.