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. Aerinite leaves a pale blue streak.
- 3Read the lusterHold the specimen under a strong light. Aerinite typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: blue, azure blue, greenish blue.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, massive, or as crusts.
Often confused with
Aerinite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Aerinite leaves pale blue, Azurite leaves light blue; luster reads dull on Aerinite and vitreous to dull on Azurite.
How to tell apart: Streak differs — Aerinite leaves pale blue, Chrysocolla leaves white; luster reads dull on Aerinite and vitreous on Chrysocolla.
How to tell apart: Aerinite is noticeably harder (Mohs 3 vs. 1.5-2); streak differs — Aerinite leaves pale blue, Vivianite leaves white to light blue; luster reads dull on Aerinite and vitreous on Vivianite.
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,Fe²⁺,Mg,Al)₂(Al,Mg,Fe³⁺)₄Si₁₂O₃₀(OH)₆·12H₂O
- Mohs hardness
- 3
- Density
- 2.2-2.3 g/cm³
- Streak
- Pale Blue
- Luster
- Dull
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, Massive, Or as Crusts
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Hydrothermal Alteration Zones in Basic Igneous Rocks
- Typical price
- $20-150 per specimen depending on intensity of blue color
Where rockhounds find aerinite
Classic worldwide localities
- Estopiñán, Huesca, Spain
- Pyrenees Mountains
- France
Field-hunting tip
Look in hydrothermal alteration zones in basic igneous rocks country — that is the host setting where aerinite typically forms. If you start seeing calcite, prehnite, quartz in float, you are in the right ground. Field specimens usually show a fibrous, massive, or as crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find aerinite on the map
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