Field identification guides for common rocks, minerals, and gemstones — using properties you can test in the field without specialized equipment.
💎 Gemstones
How to identify common gemstones in the field using hardness, luster, crystal form, and optical properties. Covers quartz varieties, garnets, tourmaline, and more.
📊 Mohs Scale
The complete guide to using the Mohs scale in the field — common field tests, what household objects to use, and hardness for 100+ minerals.
🟠 Agates
Field tests for true agate vs. look-alikes. Banding patterns, translucency testing, hardness, and fracture — how to tell agates apart from jasper, chert, and glass.
📖 Field Guide
A practical reference for common collectible minerals — identification, occurrence, associated minerals, and what to look for in the field.
🔍 Interactive
Search 40+ minerals by name, hardness value, or field test. Find out what can scratch what — instantly.
A 10x loupe, an unglazed porcelain streak plate, a set of hardness picks (or just a nail, penny, and piece of glass), and a reference book or app. The GemologyOnline and Mindat apps are excellent for field reference. Most identification can be done with just hardness and streak.
Rub the mineral across an unglazed porcelain tile (streak plate, hardness ~6.5). The color of the powder left behind is the streak — and it's often different from the mineral's surface color. Pyrite (fool's gold) has a greenish-black streak; gold has a gold-yellow streak. It's one of the most diagnostic field tests.
All quartz varieties share the same hardness (7) and chemical composition (SiO₂). They're distinguished by color and texture: amethyst (purple, crystalline), rose quartz (pink, massive), smoky quartz (brown-gray, crystalline), citrine (yellow, crystalline), and chalcedony/agate (microcrystalline, waxy).
The three decisive tests: (1) Hardness — pyrite is 6–6.5, gold is 2.5–3. A copper penny should scratch gold but not pyrite. (2) Streak — pyrite leaves a greenish-black streak, gold leaves yellow. (3) Shape — gold is malleable and will flatten; pyrite will shatter or crumble.