Edgrewite is an extremely rare calcium silicate member of the humite group found in skarn zones. It typically occurs as small, indistinct grains within limestone contact metamorphic environments, often requiring X-ray diffraction for definitive identification.
Is this edgrewite?
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 edgrewite with a known reference. Edgrewite sits at Mohs 6.5, 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.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: granular, anhedral crystals.
Often confused with
Edgrewite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Edgrewite is noticeably harder (Mohs 6.5 vs. 5-5.5).
How to tell apart: Edgrewite is noticeably harder (Mohs 6.5 vs. 3); luster reads vitreous on Edgrewite and dull on Tilleyite.
How to tell apart: Edgrewite is noticeably harder (Mohs 6.5 vs. 5.5).
Often found alongside edgrewite
Minerals reported to co-occur with edgrewite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₉Si₄O₁₆F₂
- Mohs hardness
- 6.5
- Density
- 2.918 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Granular, anhedral crystals
- Cleavage
- Good on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In xenoliths of carbonate-silicate rock altered to sanidinite facies metamorphic rock within ignimbrites
Where rockhounds find edgrewite
Classic worldwide localities
- Upper Chegem caldera, Kabardino-Balkaria, Northern Caucasus, Russia
Field-hunting tip
Where it forms: In xenoliths of carbonate-silicate rock altered to sanidinite facies metamorphic rock within ignimbrites. If you start seeing bultfonteinite, hillebrandite, jennite in float, you are in the right ground. Typical habit: granular, anhedral crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify edgrewite?+
Where is edgrewite found?+
What rocks look like edgrewite?+
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Find edgrewite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
