Gedrite is an orthorhombic amphibole typically found in regional metamorphic rocks such as amphibolites and gneisses. Collectors prize its distinct radiating fibrous or bladed habit, often occurring in association with cordierite and garnet.
Is this gedrite?
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 gedrite with a known reference. Gedrite sits at Mohs 5.5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: gray white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: brown, brown green, green, gray, gray white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: massive.
Often confused with
Gedrite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Gedrite leaves gray white, Anthophyllite leaves white or grayish.
How to tell apart: Streak differs, so Gedrite leaves gray white, Cummingtonite leaves grayish white.
How to tell apart: Streak differs, so Gedrite leaves gray white, Hornblende leaves grayish-white.
Often found alongside gedrite
Minerals reported to co-occur with gedrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- □Mg₂(Mg₃Al₂)(Si₆Al₂)O₂₂(OH)₂
- Mohs hardness
- 5.5-6
- Density
- 3.15-3.259 g/cm³
- Streak
- Gray white
- Luster
- Vitreous
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Massive
- Cleavage
- Perfect on {210}, intersecting at 54° and 126° , imperfect on {010}, {100}
- Rarity
- Uncommon
- Uses
- Collector, Scientific study
- Host rock
- Widespread in medium- to high-grade metamorphic rocks; in metasomatized contact metamorphic rocks
Where rockhounds find gedrite
Classic worldwide localities
- Haddam, Middlesex Co., Connecticut, USA
- Grafton, Oxford Co., Maine, USA
- Masons' Mountain, Macon Co., North Carolina, USA
- Powder Mill Point, Berkeley, Alameda Co., California, USA
- Strathy, Sutherlandshire, and Glen Urquhart, Inverness-shire, Scotland
- Snarum, Bjordammen, and Bamble, Norway
Field-hunting tip
Where it forms: Widespread in medium- to high-grade metamorphic rocks; in metasomatized contact metamorphic rocks. If you start seeing garnet, cordierite, hornblende in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gedrite?+
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What rocks look like gedrite?+
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Find gedrite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
