Thadeuite is a very rare phosphate mineral found primarily in complex granite pegmatites. It typically occurs as small, brownish, prismatic crystals and is visually similar to members of the apatite group, often requiring chemical analysis for definitive identification.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Thadeuite

Hardness: 5
Luster: Vitreous
Streak: White
Transparency: Transparent

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Is this thadeuite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch thadeuite with a known reference. Thadeuite sits at Mohs 5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Thadeuite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Thadeuite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellowish-brown, brown.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: prismatic crystals.

Often confused with

Thadeuite vs. its common look-alikes — and how to tell them apart in the field.

Often found alongside thadeuite

Minerals reported to co-occur with thadeuite. 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: 5
Density: 3.37 g/cm³
Colors: Yellowish-brown Brown
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Prismatic Crystals
Cleavage: Poor
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites
Typical price: $100-500 per specimen

Where rockhounds find thadeuite

Classic worldwide localities

Tip Top mine, Custer County, South Dakota, USA

Field-hunting tip

Look in granite pegmatites country — that is the host setting where thadeuite typically forms. If you start seeing triplite, apatite, rockbridgeite in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify thadeuite?+

Mohs hardness is 5. It typically shows a vitreous luster. The streak is white. Common colors include yellowish-brown, brown.

Where is thadeuite found?+

Notable localities include Tip Top mine, Custer County, South Dakota, USA.

How much is thadeuite worth?+

Typical asking prices fall in the range of $100-500 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like thadeuite?+

Thadeuite is most often confused with Apatite, Triplite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with thadeuite?+

Thadeuite commonly co-occurs with Triplite, Apatite, Rockbridgeite, Quartz. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does thadeuite form in?+

Thadeuite typically forms in granite pegmatites. Working float back to the host body is the standard way to chase a fresh occurrence.

What is thadeuite used for?+

Thadeuite is used in collector.

Find thadeuite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.