Hotsonite is a rare phosphate mineral typically occurring as massive, white, earthy to fine-grained aggregates. It is primarily found in its type locality in South Africa, often associated with weathered sedimentary phosphate deposits. Due to its limited distribution and nondescript appearance, it is primarily sought after by advanced systematic mineral collectors.
Is this hotsonite?
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 hotsonite with a known reference. Hotsonite sits at Mohs 2.5, 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 to dull, earthy.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: triclinic. Typical habit: fine-grained massive aggregates, microcrystalline.
Often confused with
Hotsonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Woodhouseite is the harder of the two (Mohs 4.5 vs. 2.5); luster reads silky to dull, earthy on Hotsonite and vitreous, pearly on {0001} on Woodhouseite.
How to tell apart: Gorceixite is the harder of the two (Mohs 6 vs. 2.5); luster reads silky to dull, earthy on Hotsonite and vitreous on Gorceixite.
How to tell apart: Crandallite is the harder of the two (Mohs 5 vs. 2.5); luster reads silky to dull, earthy on Hotsonite and vitreous, dull to chalky when massive on Crandallite.
Often found alongside hotsonite
Minerals reported to co-occur with hotsonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₅(SO₄)(PO₄)(OH)₁₀·8H₂O
- Mohs hardness
- 2.5
- Density
- 2.060-2.068 g/cm³
- Colors
- Streak
- White
- Luster
- Silky to dull, earthy
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Fine-grained massive aggregates, microcrystalline
- Cleavage
- None observed
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- A weathering product derived from natroalunite and zaherite in an arid climate (Koenabib, South Africa)
Where rockhounds find hotsonite
Classic worldwide localities
- Found in the Hotson 6 quarry, Koenabib, 65 km west of Pofadder, Cape Province, South Africa
- Blyavinski mine, Ural Mountains, Russia
Field-hunting tip
Where it forms: A weathering product derived from natroalunite and zaherite in an arid climate (Koenabib, South Africa). If you start seeing zaherite, natroalunite, sillimanite in float, you are in the right ground. Typical habit: fine-grained massive aggregates, microcrystalline. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hotsonite?+
Where is hotsonite found?+
What rocks look like hotsonite?+
What minerals are found with hotsonite?+
What kind of rock does hotsonite form in?+
What is hotsonite used for?+
Find hotsonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
