Tinsleyite is an extremely rare phosphate mineral first discovered in the phosphate-rich rocks of the Rapid Creek area. It typically occurs as small, delicate, bladed crystal clusters or crusts associated with other iron and aluminum phosphates.
Is this tinsleyite?
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 tinsleyite with a known reference. Tinsleyite 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. Streak: pink.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: dark red.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular.
Often confused with
Tinsleyite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside tinsleyite
Minerals reported to co-occur with tinsleyite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- KAl₂(PO₄)₂(OH)·2H₂O
- Mohs hardness
- ~5
- Density
- 2.69 g/cm³
- Colors
- Streak
- Pink
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Moderately abundant in highly altered triphylite pods in a complex zoned granite pegmatite (Tip Top mine, South Dakota, USA)
Where rockhounds find tinsleyite
Classic worldwide localities
- Found in the Tip Top mine, 8.5 km southwest of Custer, Custer Co., South Dakota, USA
- Sapucaia pegmatite mine, about 50 km east-southeast of Governador Valadares, Minas Gerais, Brazil
- Bendada pegmatite, near Guarda, Portugal
- Cioclovina Cave, Sureanu Mountains, Romania
- An archaeological site, Santana do Riacho, ~90 km north of Belo Horizonte, Minas Gerais, Brazil
Field-hunting tip
Where it forms: Moderately abundant in highly altered triphylite pods in a complex zoned granite pegmatite (Tip Top mine, South Dakota, USA). If you start seeing leucophosphite, triphylite, rockbridgeite-frondelite in float, you are in the right ground. Typical habit: tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tinsleyite?+
Where is tinsleyite found?+
What rocks look like tinsleyite?+
What minerals are found with tinsleyite?+
What kind of rock does tinsleyite form in?+
What is tinsleyite used for?+
Find tinsleyite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
