Tacharanite is a rare calcium silicate mineral typically found as white, platy, or scaly aggregates within basalt cavities. It is often discovered in association with other zeolite-group minerals and calcium silicates in altered volcanic environments. Collectors prize it for its specific paragenesis within restricted geological sites like the Isle of Skye.
Is this tacharanite?
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 tacharanite with a known reference. Tacharanite sits at Mohs 5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to dull.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: cryptocrystalline.
Often confused with
Tacharanite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside tacharanite
Minerals reported to co-occur with tacharanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₁₂Al₂Si₁₈O₅₇(OH)₁₀·~4H₂O
- Mohs hardness
- 5
- Density
- 2.33-2.36 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous to dull
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Cryptocrystalline
- Cleavage
- {001}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In amygdules and fractures in metabasalts and basaltic breccias; in hydrothermally altered quartzite inclusions in basalt (Bramburg, Germany)
Where rockhounds find tacharanite
Classic worldwide localities
- North of Portree, Isle of Skye, Scotland
- Isle of Mull, Scotland
- Binbill quarry, Cairnie, Huntley, Aberdeenshire, Scotland
- Carneal, Co. Antrim, Ireland
- Bramburg, near Göttingen, Lower Saxony, and at Arensberg, near Zilsdorf, Eifel district, Germany
- Espalion, Aveyron, France
Field-hunting tip
Where it forms: In amygdules and fractures in metabasalts and basaltic breccias; in hydrothermally altered quartzite inclusions in basalt (Bramburg, Germany). If you start seeing tobermorite, gyrolite, mesolite in float, you are in the right ground. Typical habit: cryptocrystalline. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tacharanite?+
Where is tacharanite found?+
What rocks look like tacharanite?+
What minerals are found with tacharanite?+
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What is tacharanite used for?+
Find tacharanite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
