mineral
Likely tumbled black stone or glassy mineral
Indeterminate from image; possibilities include obsidian, hematite, or black tourmaline
AI-generated identification · may be incorrectSmall, dark gray-black, smooth and highly reflective with irregular rounded surfaces; hardness and crystal structure cannot be determined visually. Apparent glassy luster may indicate obsidian, but the image is insufficient for reliable identification.
Identified More mineral →
Explore Likely tumbled black stone or glassy mineral in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Small, dark gray-black, smooth and highly reflective with irregular rounded surfaces; hardness and crystal structure cannot be determined visually. Apparent glassy luster may indicate obsidian, but the image is insufficient for reliable identification.
Formation & geological history
If obsidian, it is volcanic glass formed by rapid cooling of silica-rich lava, generally Quaternary to older Cenozoic. Hematite or tourmaline would form in hydrothermal, igneous, or metamorphic environments.
Uses & applications
Obsidian is used for ornaments and historically sharp tools; hematite is an iron ore and lapidary material; black tourmaline is used in jewelry and mineral collecting.
Geological facts
A streak, hardness test, and examination of fracture surfaces are needed to distinguish these materials. Obsidian commonly shows conchoidal fracture, hematite leaves a red-brown streak, and tourmaline commonly has prismatic striated crystals.
Field identification & locations
Common sources include volcanic regions for obsidian, iron-rich rocks worldwide for hematite, and granitic or metamorphic terrains for tourmaline. Avoid destructive testing if it is a valuable polished specimen.
