Aerinite is a rare and visually striking silicate mineral known for its intense blue color that often stains surrounding rocks. It typically occurs as fibrous aggregates or crusts filling fractures in altered basaltic rocks. It is most famous for its occurrence in the Pyrenees region, where it was historically used as a pigment in Romanesque frescoes.
Is this aerinite?
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 aerinite with a known reference. Aerinite sits at Mohs ~3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: bluish white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: blue, blue green, sky blue.
- 5Look at form & habitCrystal system: trigonal. Typical habit: fibrous.
Often confused with
Aerinite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Aerinite leaves bluish white, Azurite leaves pale blue.
How to tell apart: Streak differs, so Aerinite leaves bluish white, Chrysocolla leaves white when pure.
How to tell apart: Aerinite is noticeably harder (Mohs ~3 vs. 1.5-2); streak differs, so Aerinite leaves bluish white, Vivianite leaves white, altering to dark blue, brown.
Often found alongside aerinite
Minerals reported to co-occur with aerinite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ca,Na)₆(Fe,Fe,Mg,Al)₄(Al,Mg)₆Si₁₂O₃₆(OH)₁₂(CO₃)·12H₂O
- Mohs hardness
- ~3
- Density
- 2.48 g/cm³
- Colors
- Streak
- Bluish white
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Trigonal
- Crystal habit
- Fibrous
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A hydrothermal mineral of the zeolite facies, formed at relatively low temperature, in fractures cutting mafic igneous rocks (Saint-Pandelon, France)
Where rockhounds find aerinite
Classic worldwide localities
- Gunsight Mountains, Pima Co., Arizona, USA
- Caserras, Juseu, and Estopiñan, Huesca Province, Spain
- Tartaren, Lerida Province, Spain
- Saint-Pandelon, Landes, France
- Ourika, Morocco
Field-hunting tip
Where it forms: A hydrothermal mineral of the zeolite facies, formed at relatively low temperature, in fractures cutting mafic igneous rocks (Saint-Pandelon, France). If you start seeing prehnite, scolecite, mesolite in float, you are in the right ground. Typical habit: fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify aerinite?+
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What rocks look like aerinite?+
What minerals are found with aerinite?+
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Find aerinite on the map
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