Martinite is a rare member of the garnet-related group occurring as small, equant crystals. It is primarily found in metasomatized ultramafic rocks known as rodingites. Collectors value it for its rarity and its distinct crystal structure compared to more common silicate minerals.
Is this martinite?
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 martinite with a known reference. Martinite sits at Mohs 4, 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.
- 4Match the color rangeCompare against the expected color range: colorless, purple.
- 5Look at form & habitCrystal system: triclinic. Typical habit: equant crystals.
Often confused with
Martinite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside martinite
Minerals reported to co-occur with martinite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,☐,Ca)₁₂Ca₄(Si,S,B)₁₄B₂O₃₈(OH,Cl)₂F₂(H₂O)₄
- Mohs hardness
- 4
- Density
- 2.55 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Equant crystals
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Formed through the interaction of highly fractionated, hyperagpaitic fluids with sodalite syenite xenoliths. (reyerite group; structure)
Where rockhounds find martinite
Classic worldwide localities
- Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada (type locality)
Field-hunting tip
Where it forms: Formed through the interaction of highly fractionated, hyperagpaitic fluids with sodalite syenite xenoliths. (reyerite group; structure). If you start seeing calcite, diopside, grossular in float, you are in the right ground. Typical habit: equant crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify martinite?+
Where is martinite found?+
What rocks look like martinite?+
What minerals are found with martinite?+
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What is martinite used for?+
Find martinite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
