Tobermorite is a calcium silicate hydrate mineral often found as a secondary mineral in altered volcanic rocks or contact-metamorphosed limestone. Collectors typically look for its characteristic pearly, thin, platy or fibrous white to pinkish clusters that form in vugs or cavities.
Is this tobermorite?
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 tobermorite with a known reference. Tobermorite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Tobermorite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Tobermorite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, pink, yellowish, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals, fibrous, massive, or as coating.
Often confused with
Tobermorite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Pectolite is the harder of the two (Mohs 4.5-5 vs. 2.5); luster reads pearly on Tobermorite and vitreous to silky on Pectolite.
How to tell apart: Prehnite is the harder of the two (Mohs 6-6.5 vs. 2.5); luster reads pearly on Tobermorite and vitreous on Prehnite.
Often found alongside tobermorite
Minerals reported to co-occur with tobermorite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₅Si₆O₁₆(OH)₂·4H₂O
- Mohs hardness
- 2.5
- Density
- 2.4-2.5 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy Crystals, Fibrous, Massive, Or as Coating
- Cleavage
- Perfect Basal
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research
- Host rock
- Metamorphic Rocks, Hydrothermal Veins in Basalt, And Thermally Metamorphosed Limestone
- Typical price
- $10-60 for small mineral specimens
Where rockhounds find tobermorite
Classic worldwide localities
- Tobermory, Scotland
- Giurudden, Sweden
- Crestmore, California, USA
- Mount Vesuvius, Italy
Field-hunting tip
Look in metamorphic rocks, hydrothermal veins in basalt, and thermally metamorphosed limestone country — that is the host setting where tobermorite typically forms. If you start seeing calcite, ettringite, portlandite in float, you are in the right ground. Field specimens usually show a platy crystals, fibrous, massive, or as coating habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tobermorite?+
Where is tobermorite found?+
How much is tobermorite worth?+
What rocks look like tobermorite?+
What minerals are found with tobermorite?+
What kind of rock does tobermorite form in?+
What is tobermorite used for?+
Find tobermorite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
