Grossite is a very rare calcium aluminate mineral primarily found in refractory inclusions within certain meteorites. It typically occurs as small, colorless grains and represents an early-forming condensate from the solar nebula. Identifying it usually requires professional analytical equipment due to its extreme rarity and small crystal size.
Is this grossite?
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 grossite with a known reference. Grossite sits at Mohs 6, 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, white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: anhedral grains, small inclusions.
Often confused with
Grossite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside grossite
Minerals reported to co-occur with grossite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaAl₄O₇
- Mohs hardness
- 6
- Density
- 2.88 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Anhedral grains, small inclusions
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- In argillaceous limestones metamorphosed at high temperature and low pressure (Hatrurim Formation, Israel); in Ca–Al-rich inclusions thought formed by condensation from a hot gas or molten droplets (meteorites)
Where rockhounds find grossite
Classic worldwide localities
- Hatrurim Formation, Israel
- Chondritic meteorites Acfer 182, Acfer 059-El Djouf 001, ALH85085
Field-hunting tip
Where it forms: In argillaceous limestones metamorphosed at high temperature and low pressure (Hatrurim Formation, Israel); in Ca–Al-rich inclusions thought formed by condensation from a hot gas or molten droplets (meteorites). If you start seeing brownmillerite, mayenite, larnite in float, you are in the right ground. Typical habit: anhedral grains, small inclusions. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify grossite?+
Where is grossite found?+
What rocks look like grossite?+
What minerals are found with grossite?+
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Find grossite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
