How to Identify Rocks and Minerals: A Beginner's Guide

Rock and mineral identification sounds technical but most common specimens can be identified using a handful of physical properties you can assess with your eyes and basic tools.

Colour

Colour is useful but unreliable on its own — many minerals appear in multiple colours, and surface weathering can change appearance. Use colour as a starting point, not a conclusion.

Streak

Scrape the specimen across unglazed white porcelain (a streak plate) and observe the colour of the powder it leaves. Streak is more consistent than surface colour because it reflects the true mineral colour. Hematite, which can appear black or silver on the surface, always leaves a reddish-brown streak.

Hardness

The Mohs scale rates hardness from 1 (talc) to 10 (diamond). You can estimate hardness with everyday items: a fingernail scratches minerals up to hardness 2.5; a copper coin scratches up to 3.5; a steel knife scratches up to 6.5. If a mineral scratches glass (hardness ~5.5), it's harder than 5.5.

Luster

How does the surface reflect light? Metallic luster (like a metal surface) indicates iron sulphides or native metals. Glassy or vitreous luster is common in quartz. Waxy, resinous, pearly — each has diagnostic value.

Cleavage and fracture

Cleavage is the tendency to break along flat planes. Mica cleaves into thin sheets; calcite has three directions of perfect cleavage. Fracture is breakage in irregular patterns. Quartz has conchoidal (shell-like) fracture rather than cleavage. These are among the most diagnostic properties for identification.