Eylettersite is a rare phosphate-sulfate mineral member of the woodhouseite group, primarily known as a secondary mineral in uranium-bearing pegmatites. It typically occurs as minute, crust-like or massive aggregates and is of interest primarily to advanced systematic mineral collectors due to its radioactive nature and scarcity.

Hardness

3-4

Mohs

Luster

Vitreous

Streak

White

Transparency

Semitransparent

mineralrareWoodhouseite Group family

Eylettersite

Hardness: 3-4
Luster: Vitreous
Streak: White
Transparency: Semitransparent

Is this eylettersite?

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 eylettersite with a known reference. Eylettersite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: cream white.
5
Look at form & habit
Crystal system: trigonal. Typical habit: nodular, pulverulent.

Often confused with

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

mineral

Crandallite

Mohs 5

How to tell apart: Crandallite is the harder of the two (Mohs 5 vs. 3-4).

How to tell apart: Gorceixite is the harder of the two (Mohs 6 vs. 3-4).

Compare →

Often found alongside eylettersite

Minerals reported to co-occur with eylettersite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Th₀.₇₅Al₃(PO₄)₂(OH)₆
Mohs hardness: 3-4
Density: 3.38-3.44 g/cm³
Colors: Cream white
Streak: White
Luster: Vitreous
Transparency: Semitransparent
Crystal system: Trigonal
Crystal habit: Nodular, pulverulent
Cleavage: None
Fluorescence: Greenish yellow under SW UV; weak cream brown under LW UV
Rarity: Rare
Uses: Collector
Host rock: An alteration product of thorian crandallite in a phosphate-rich granite pegmatite

Where rockhounds find eylettersite

Classic worldwide localities

Kobokobo pegmatite, Lusungu River district, Kivu Province, Congo (Zaire)

Field-hunting tip

Where it forms: An alteration product of thorian crandallite in a phosphate-rich granite pegmatite. If you start seeing autunite, phosphuranylite, fluorapatite in float, you are in the right ground. Typical habit: nodular, pulverulent. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify eylettersite?+

Mohs hardness is 3-4. Luster: vitreous. The streak is white. Common colors include cream white.

Where is eylettersite found?+

Notable localities include Kobokobo pegmatite, Lusungu River district, Kivu Province, Congo (Zaire).

Is eylettersite safe to handle?+

Eylettersite contains uranium or thorium and calls for real care. Contains thorium, which is radioactive. Handle with care, wash hands after handling, and store in a lead-lined container or away from other specimens.

What rocks look like eylettersite?+

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

What minerals are found with eylettersite?+

Eylettersite commonly co-occurs with Autunite, Phosphuranylite, Fluorapatite, Limonite, Feldspar, Cyrtolite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does eylettersite form in?+

Where it forms: An alteration product of thorian crandallite in a phosphate-rich granite pegmatite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is eylettersite used for?+

Eylettersite is used in collector.

Find eylettersite on the map

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