Fact Sheet

• Chemical formula: Zn₂(AsO₄)(OH)

• Mineral class/group: Arsenate mineral; olivenite group

• Crystal system: Orthorhombic

• Mohs hardness: 3.5

• Luster: Usually vitreous; sometimes sub-vitreous, waxy, or greasy

• Streak: White

• Typical colors: Colorless to white in ideal form; commonly yellow to honey-yellow, green, blue-green, rose, pink, purple, or zoned

• Notable localities: Ojuela Mine, Mapimí, Mexico; Lavrion/Laurium, Greece; Tsumeb, Namibia; Cap Garonne, France; Chañarcillo, Chile

• Main value: Collector specimens; rarely faceted as a collector gemstone

What Is Adamite?

Adamite is a zinc arsenate hydroxide mineral with the formula Zn₂(AsO₄)(OH). It is not an everyday rock-forming mineral. Instead, it is a secondary mineral that forms in the oxidized parts of zinc ore deposits where arsenic is also present.

Collectors value adamite because it can grow as bright, glassy crystals in unusually vivid colors: honey-yellow, lime green, blue-green, pink, violet, and sometimes color-zoned combinations of several shades. Adamite is not important as an industrial mineral. Its value lies in its beauty, rarity, and the story it tells about the chemistry of weathered ore deposits.

How Adamite Forms

Adamite usually forms in the oxidized zone of zinc- and arsenic-bearing ore deposits. This is the near-surface part of an ore body where oxygen-rich groundwater reacts with older ore minerals. During weathering, zinc and arsenate can be released, transported over short distances, and then re-precipitated as secondary minerals such as adamite.

This is why adamite is often found with other secondary ore-zone minerals, including calcite, smithsonite, hemimorphite, goethite/limonite, scorodite, mimetite, conichalcite, and other zinc, copper, iron, and arsenate minerals. Its presence tells a geologist that zinc, arsenic, oxygen-rich water, and near-surface weathering have interacted. Adamite is not a deep-Earth mineral; it is a mineral of altered ore deposits.

Why Adamite Has So Many Colors

In its pure form, adamite can be colorless to white, but many collector specimens owe their color to minor substitutions or impurities.

• Yellow to honey-yellow adamite is common and may be influenced by iron.
• Green to blue-green adamite is commonly associated with copper-bearing compositions, although older labels such as “cuprian adamite” should be used carefully because some specimens once described that way may actually be zincolivenite.
• Pink, rose, violet, or purple adamite can be related to cobalt or manganese.
• Blue and blue-green specimens are especially prized by collectors, including material from classic districts such as Lavrion/Laurium in Greece.

Adamite may also fluoresce under ultraviolet light, sometimes showing a strong green or lemon-yellow glow. This fluorescence is one reason it is especially popular among mineral collectors.

Important Localities

The Ojuela Mine at Mapimí, Durango, Mexico, is one of the classic localities for adamite and has produced many of the specimens most familiar to collectors, especially yellow to green crystals on iron-rich matrix. Other important localities include the Lavrion/Laurium mining district in Greece, known for green to blue-green material; Tsumeb in Namibia, famous for unusual and highly collectible mineral specimens; Cap Garonne in France; and Chañarcillo in Chile, the type locality for adamite.

Uses and Collecting

Adamite has no major industrial use. Its main value is as a mineral specimen: it is colorful, sometimes fluorescent, and often forms attractive crystal clusters. It is occasionally faceted as a small collector gemstone, but it is poorly suited to normal jewelry. With a Mohs hardness of only 3.5, brittle tenacity, and good cleavage, faceted adamite is better treated as a collector curiosity than as a wearable gem.

Safety Note

Adamite contains arsenate in its chemical structure. Normal handling of a stable mineral specimen is not the same as handling a soluble arsenic compound, but sensible precautions still apply: do not grind it, inhale dust, lick it, or place it in water meant for drinking. Wash your hands after handling, especially before eating.