Thérèsemagnanite is a rare cobalt-bearing sulfate mineral typically found as delicate, bright blue platy crystals or crusts. It is primarily known from the historic cobalt mining district of Bou Azzer in Morocco, where it forms as a secondary mineral in oxidation zones.
Is this thérèsemagnanite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch thérèsemagnanite with a known reference. Thérèsemagnanite sits at Mohs 2-3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Thérèsemagnanite leaves a pale blue streak.
- 3Read the lusterHold the specimen under a strong light. Thérèsemagnanite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue, greenish blue.
- 5Look at form & habitCrystal system: trigonal. Typical habit: platy crystals, crusts.
Often confused with
Thérèsemagnanite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside thérèsemagnanite
Minerals reported to co-occur with thérèsemagnanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Co₆Al₃(SO₄)₂(OH)₁₈·12H₂O
- Mohs hardness
- 2-3
- Density
- 3.32 g/cm³
- Colors
- Streak
- Pale Blue
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Platy Crystals, Crusts
- Cleavage
- Perfect Basal
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Veins in Serpentinite
- Typical price
- $50-300+ depending on size and quality
Where rockhounds find thérèsemagnanite
Classic worldwide localities
- Bou Azzer, Morocco
Field-hunting tip
Look in hydrothermal veins in serpentinite country — that is the host setting where thérèsemagnanite typically forms. If you start seeing cobaltite, skutterudite, erythrite in float, you are in the right ground. Field specimens usually show a platy crystals, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify thérèsemagnanite?+
Where is thérèsemagnanite found?+
How much is thérèsemagnanite worth?+
What rocks look like thérèsemagnanite?+
What minerals are found with thérèsemagnanite?+
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Find thérèsemagnanite on the map
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