Taniajacoite is a rare copper-arsenic mineral characterized by its distinct green, platy crystal morphology. It is primarily found in the oxidized zones of copper-arsenic rich hydrothermal deposits, typically appearing as small, delicate clusters.

Hardness

3-4

Mohs

Luster

Vitreous

Streak

Pale Green

Transparency

Translucent

mineralrare

Taniajacoite

Hardness: 3-4
Luster: Vitreous
Streak: Pale Green
Transparency: Translucent

No image

Is this taniajacoite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch taniajacoite with a known reference. Taniajacoite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Taniajacoite leaves a pale green streak.
3
Read the luster
Hold the specimen under a strong light. Taniajacoite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: dark green, blackish-green.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: platy crystals.

Often confused with

Taniajacoite vs. its common look-alikes — and how to tell them apart in the field.

mineral

Austinite

Mohs 4

How to tell apart: Streak differs — Taniajacoite leaves pale green, Austinite leaves white.

How to tell apart: Streak differs — Taniajacoite leaves pale green, Conichalcite leaves light green.

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All properties

Chemical formula: CaCu₄(AsO₄)₂(OH)₄·5H₂O
Mohs hardness: 3-4
Density: 2.95 g/cm³
Colors: Dark Green Blackish-green
Streak: Pale Green
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Platy Crystals
Cleavage: Perfect
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Veins
Typical price: $50-300 per specimen

Where rockhounds find taniajacoite

Classic worldwide localities

Taniajaco mine, Mexico

Field-hunting tip

Look in hydrothermal veins country — that is the host setting where taniajacoite typically forms. If you start seeing arsenates, copper secondary minerals in float, you are in the right ground. Field specimens usually show a platy crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify taniajacoite?+

Mohs hardness is 3-4. It typically shows a vitreous luster. The streak is pale green. Common colors include dark green, blackish-green.

Where is taniajacoite found?+

Notable localities include Taniajaco mine, Mexico.

How much is taniajacoite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is taniajacoite safe to handle?+

It contains toxic constituents. Contains arsenic and copper; avoid ingestion, inhalation of dust, or skin contact. Wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like taniajacoite?+

Taniajacoite is most often confused with Austinite, Conichalcite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with taniajacoite?+

Taniajacoite commonly co-occurs with Arsenates, Copper secondary minerals. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does taniajacoite form in?+

Taniajacoite typically forms in hydrothermal veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is taniajacoite used for?+

Taniajacoite is used in collector.

Find taniajacoite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.