Dorrite is an extremely rare mineral belonging to the sapphirine group, primarily found in pyrometamorphic environments. It typically occurs as small anhedral grains in association with magnetite and other oxides, requiring advanced petrographic methods for positive identification.
Is this dorrite?
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 dorrite with a known reference. Dorrite sits at Mohs 5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Dorrite leaves a gray streak.
- 3Read the lusterHold the specimen under a strong light. Dorrite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brown.
- 5Look at form & habitCrystal system: triclinic. Typical habit: anhedral grains.
Often confused with
Dorrite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Sapphirine is the harder of the two (Mohs 7.5 vs. 5); streak differs, so Dorrite leaves gray, Sapphirine leaves white; luster reads submetallic on Dorrite and vitreous on Sapphirine.
How to tell apart: Streak differs, so Dorrite leaves gray, Aenigmatite leaves reddish-brown; luster reads submetallic on Dorrite and vitreous on Aenigmatite.
Often found alongside dorrite
Minerals reported to co-occur with dorrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₄Mg₄Fe₄³⁺Al₄(Al₄Si₂)O₂₀
- Mohs hardness
- 5
- Density
- 3.55 g/cm³
- Streak
- Gray
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Triclinic
- Crystal habit
- Anhedral Grains
- Cleavage
- Good On {010} and {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Metamorphic Rocks of The Pyrometamorphic Facies
Where rockhounds find dorrite
Classic worldwide localities
- Durham ranch, 25 km south of Gillette, Powder River Basin, Wyoming, USA
Field-hunting tip
Look in metamorphic rocks of the pyrometamorphic facies country, the host setting where dorrite typically forms. If you start seeing magnetite, gehlenite, perovskite in float, you are in the right ground. Field specimens usually show a anhedral grains habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find dorrite on the map
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