Mcallisterite is a rare magnesium borate mineral typically found as small, clear, tabular crystals in borate-rich evaporite deposits. Collectors primarily find it associated with other borate minerals in the Kramer deposit of California. It is notable for its low hardness and specific gravity, often requiring careful handling and storage to prevent dehydration.
Is this mcallisterite?
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 mcallisterite with a known reference. Mcallisterite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Mcallisterite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Mcallisterite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: tabular crystals, massive, granular.
Often confused with
Mcallisterite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Priceite is the harder of the two (Mohs 3-3.5 vs. 2); luster reads vitreous on Mcallisterite and dull on Priceite.
How to tell apart: Luster reads vitreous on Mcallisterite and vitreous to pearly on Kernite.
How to tell apart: Howlite is the harder of the two (Mohs 3.5 vs. 2); luster reads vitreous on Mcallisterite and subvitreous on Howlite.
Often found alongside mcallisterite
Minerals reported to co-occur with mcallisterite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₂(B₆O₇(OH)₆)₂·9H₂O
- Mohs hardness
- 2
- Density
- 2.05 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Tabular Crystals, Massive, Granular
- Cleavage
- Distinct On {10-14}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Borate Deposits in Sedimentary Basins
- Typical price
- $20-150 thumbnail
Where rockhounds find mcallisterite
Classic worldwide localities
- Kramer deposit, Boron, California, USA
- Tincalayu mine, Salta, Argentina
Field-hunting tip
Look in borate deposits in sedimentary basins country — that is the host setting where mcallisterite typically forms. If you start seeing borax, kernite, colemanite in float, you are in the right ground. Field specimens usually show a tabular crystals, massive, granular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find mcallisterite on the map
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