Martinandresite is an extremely rare calcium-yttrium silicate mineral found almost exclusively in the alkaline rocks of Mont Saint-Hilaire. It typically occurs as delicate, acicular, or fibrous aggregates often associated with other rare silicate minerals in vugs and cavities.
Is this martinandresite?
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 martinandresite with a known reference. Martinandresite sits at Mohs 3-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Martinandresite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Martinandresite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular crystals, radial aggregates.
Often confused with
Martinandresite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside martinandresite
Minerals reported to co-occur with martinandresite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₄Y₂Si₄O₁₃(OH)₂·2H₂O
- Mohs hardness
- 3-4
- Density
- 3.36 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular Crystals, Radial Aggregates
- Cleavage
- Distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Alkaline Igneous Intrusions
- Typical price
- $50-300+ per specimen
Where rockhounds find martinandresite
Classic worldwide localities
- Mont Saint-Hilaire, Quebec, Canada
Field-hunting tip
Look in alkaline igneous intrusions country — that is the host setting where martinandresite typically forms. If you start seeing analcime, sodalite, microcline in float, you are in the right ground. Field specimens usually show a acicular crystals, radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find martinandresite on the map
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