Hillite is a rare phosphate mineral in the hopeite group that occurs in oxidized zinc deposits. It typically forms small, clear, tabular crystals or radiating sprays that are visually indistinguishable from hopeite without X-ray diffraction analysis.
Is this hillite?
4-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 hillite with a known reference. Hillite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
- 2Read the lusterHold the specimen under a strong light. Luster: vitreous; silky aggregates.
- 3Match the color rangeCompare against the expected color range: colorless, gray, greenish gray, bluish gray.
- 4Look at form & habitCrystal system: triclinic. Typical habit: blocky.
Often confused with
Hillite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside hillite
Minerals reported to co-occur with hillite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂Zn(PO₄)₂·2H₂O
- Mohs hardness
- 3.5
- Density
- 3.16 g/cm³
- Luster
- Vitreous; silky aggregates
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
- Crystal habit
- Blocky
- Cleavage
- Perfect on {010} and {001}
- Fluorescence
- Weak greenish yellow fluorescence in SW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In a gossan developed on argillaceous siltstone
Where rockhounds find hillite
Classic worldwide localities
- Reaphook Hill, Flinders Ranges, South Australia, Australia
Field-hunting tip
Where it forms: In a gossan developed on argillaceous siltstone. If you start seeing zincian collinsite, scholzite in float, you are in the right ground. Typical habit: blocky. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hillite?+
Where is hillite found?+
What rocks look like hillite?+
What minerals are found with hillite?+
What kind of rock does hillite form in?+
What is hillite used for?+
Find hillite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
