Calaverite Identification Guide

What Calaverite Looks Like

Calaverite is a gold telluride (AuTe2) and one of the few common ores in which gold is locked in a mineral rather than free. It is metallic with a brassy to silvery-yellow color, sometimes with a slight greenish or bronze cast. It is opaque, with a bright metallic luster on fresh surfaces that can tarnish duller. Crystals are typically small, bladed, striated, or lath-like, but it most often occurs as grains, masses, and veinlets in quartz. It is much denser and more brittle than its appearance suggests.

Step-by-Step Field-ID Checklist

1. Note the brassy metallic color in quartz or sulfide-rich vein material.
2. Heft the specimen — calaverite is notably heavy due to gold and tellurium.
3. Test scratch/streak — it leaves a greenish-gray to yellowish streak, not the black of pyrite or sulfides.
4. Check brittleness — it is brittle and crushes to powder; it does not flatten or smear like native gold.
5. Look for association with quartz, fluorite, pyrite, and other tellurides in low-temperature gold veins.
6. If possible, a blowpipe/flame test produces a garlic odor (tellurium) and a gold bead — a classic confirmation.

Key Diagnostic Tests

• Mohs hardness: 2.5–3 — soft; can be scratched by a knife.
• Streak: greenish-gray to yellowish.
• Cleavage: none; fracture uneven, mineral is brittle.
• Density: very high, about 9.1–9.4 g/cm3 — strikingly heavy.
• Not magnetic.
• Tellurium test: heating releases a characteristic garlic-like odor and leaves a malleable gold residue.

Common Look-Alikes and How to Tell Them Apart

• Native gold: gold is malleable (flattens, will not powder), has a yellow streak, and is even denser (~19 g/cm3). Calaverite is brittle and crushes — the single best field discriminator.
• Pyrite ("fool's gold"): pyrite is harder (6–6.5), gives a black/greenish-black streak, and is paler brass; calaverite is soft and gives a greenish-gray streak.
• Chalcopyrite: more golden-to-iridescent, softer than pyrite but gives a greenish-black streak, and lacks calaverite's extreme density.
• Sylvanite (another Au-Ag telluride): very similar; sylvanite is more silvery and commonly shows distinct bladed/cleavable crystals and good cleavage, whereas calaverite lacks cleavage.
• Marcasite: pale, brittle, but lighter and gives a dark streak.

Where Calaverite Is Typically Found

Calaverite is named for Calaveras County, California, and is a key ore at famous epithermal gold-telluride districts: Cripple Creek, Colorado; Kalgoorlie, Western Australia; and parts of Romania (Transylvania). It forms in low-temperature hydrothermal gold veins, usually with quartz, fluorite, pyrite, and other tellurides.