Isokite is a rare phosphate mineral typically found in complex granite pegmatites. It is often identified by its association with secondary phosphate minerals and its distinct monoclinic crystal structure, though it is usually found in massive or granular form.
Is this isokite?
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 isokite with a known reference. Isokite sits at Mohs 4.5-5, 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: silky (fibers), slightly pearly (plates).
- 4Match the color rangeCompare against the expected color range: colorless, gray pink, pink.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive.
Often confused with
Isokite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads silky (fibers), slightly pearly (plates) on Isokite and vitreous to greasy, pearly on good cleavages on Amblygonite.
How to tell apart: Luster reads silky (fibers), slightly pearly (plates) on Isokite and resinous on Monazite.
How to tell apart: Luster reads silky (fibers), slightly pearly (plates) on Isokite and vitreous on Apatite.
Often found alongside isokite
Minerals reported to co-occur with isokite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaMg(PO₄)F
- Mohs hardness
- 4.5-5
- Density
- 3.15-3.27 g/cm³
- Streak
- White
- Luster
- Silky (fibers), slightly pearly (plates)
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Massive
- Cleavage
- Very good on {010}
- Fluorescence
- Blue under LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A late-stage metasomatic mineral in ankeritic carbonatite (Nkombwa Hill); replacing wagnerite in a pegmatite dike in sillimanite grade gneiss (Benson mines)
Where rockhounds find isokite
Classic worldwide localities
- Benson Mines, near Star Lake, St. Lawrence Co., New York, USA
- Nkombwa Hill, 24 km east of Isoka, Zambia
- Horní Slavkov (Schlaggenwald), Czech Republic
- Mangualde pegmatite, near Mesquitela, from Folgorinho, from Senhora de Assunção quarry, at Aldeia Nova, Satao, and in the Ribeira and Panasqueira Sn-W deposits, Portugal
- Bayan Obo Fe-Nb-RE deposit, 130 km north of Baotou, Inner Mongolia, China
- Brumado, Bahia, Brazil
Field-hunting tip
Where it forms: A late-stage metasomatic mineral in ankeritic carbonatite (Nkombwa Hill); replacing wagnerite in a pegmatite dike in sillimanite grade gneiss (Benson mines). If you start seeing dolomite, strontian fluorapatite, monazite 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 isokite?+
Where is isokite found?+
What rocks look like isokite?+
What minerals are found with isokite?+
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What is isokite used for?+
Find isokite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
