Sainfeldite is a rare hydrated calcium arsenate mineral typically found as tabular crystals or crusts in hydrothermal veins. It is most recognized for its occurrence in the mining districts of Sainte-Marie-aux-Mines, where it forms in association with other arsenic-rich species.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Sainfeldite

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this sainfeldite?

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 sainfeldite with a known reference. Sainfeldite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Sainfeldite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Sainfeldite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white, pale pink.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals, crusts.

Often confused with

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

mineral

Pharmacosiderite

Mohs 2.5

How to tell apart: Luster reads vitreous on Sainfeldite and adamantine on Pharmacosiderite.

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Often found alongside sainfeldite

Minerals reported to co-occur with sainfeldite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Ca₅(AsO₃OH)₂(AsO₄)₂·4H₂O
Mohs hardness: 2
Density: 3.32 g/cm³
Colors: Colorless White Pale Pink
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular Crystals, Crusts
Cleavage: Perfect On {010}
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Veins
Typical price: $50-300 per specimen

Where rockhounds find sainfeldite

Classic worldwide localities

Sainte-Marie-aux-Mines, France
Bou Azzer, Morocco

Field-hunting tip

Look in hydrothermal veins country — that is the host setting where sainfeldite typically forms. If you start seeing calcite, dolomite, arsenopyrite in float, you are in the right ground. Field specimens usually show a tabular crystals, crusts habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify sainfeldite?+

Mohs hardness is 2. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white, pale pink.

Where is sainfeldite found?+

Notable localities include Sainte-Marie-aux-Mines, France; Bou Azzer, Morocco.

How much is sainfeldite 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 sainfeldite safe to handle?+

It contains toxic constituents. Contains arsenic, which is highly toxic. Handle with care, avoid inhalation of dust, and wash hands thoroughly after handling specimens. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like sainfeldite?+

Sainfeldite is most often confused with Pharmacosiderite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with sainfeldite?+

Sainfeldite commonly co-occurs with Calcite, Dolomite, Arsenopyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does sainfeldite form in?+

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

What is sainfeldite used for?+

Sainfeldite is used in collector.

Find sainfeldite on the map

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