Weeksite is a distinctive radioactive uranium mineral typically found as radiating clusters of yellow, fan-shaped crystals or crusts. It is highly prized by collectors of radioactive species for its vibrant yellow-green fluorescence under ultraviolet light.

Hardness

Mohs

Luster

Pearly

Streak

Yellow

Transparency

Translucent

mineralrareUranyl silicate group family

Weeksite

Hardness: 2
Luster: Pearly
Streak: Yellow
Transparency: Translucent

Is this weeksite?

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 weeksite with a known reference. Weeksite sits at Mohs 2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Weeksite leaves a yellow streak.
3
Read the luster
Hold the specimen under a strong light. Weeksite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: yellow, pale yellow.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: radiating globular aggregates, crusts, fan-shaped sprays.

Often confused with

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

mineral

Boltwoodite

Mohs 3.5

How to tell apart: Boltwoodite is the harder of the two (Mohs 3.5 vs. 2).

How to tell apart: Soddyite is the harder of the two (Mohs 3.5 vs. 2); luster reads pearly on Weeksite and vitreous on Soddyite.

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Often found alongside weeksite

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

All properties

Chemical formula: K₂(UO₂)₂(Si₂O₅)₃·4H₂O
Mohs hardness: 2
Density: 3.9-4.1 g/cm³
Colors: Yellow Pale Yellow
Streak: Yellow
Luster: Pearly
Transparency: Translucent
Crystal system: Orthorhombic
Crystal habit: Radiating Globular Aggregates, Crusts, Fan-shaped Sprays
Cleavage: Perfect
Fluorescence: Bright Yellow-green Under UV
Rarity: Rare
Uses: Collector, Scientific Research
Host rock: Rhyolitic Volcanic Rocks, Hydrothermal Veins
Typical price: $30-200 depending on specimen size and radioactivity levels

Where rockhounds find weeksite

Classic worldwide localities

Thomas Range, Utah, USA
Wheeler County, Georgia, USA
Kazakhstan

Field-hunting tip

Look in rhyolitic volcanic rocks, hydrothermal veins country — that is the host setting where weeksite typically forms. If you start seeing fluorite, quartz, chalcedony in float, you are in the right ground. Field specimens usually show a radiating globular aggregates, crusts, fan-shaped sprays habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify weeksite?+

Mohs hardness is 2. It typically shows a pearly luster. The streak is yellow. Common colors include yellow, pale yellow.

Where is weeksite found?+

Notable localities include Thomas Range, Utah, USA; Wheeler County, Georgia, USA; Kazakhstan.

How much is weeksite worth?+

Typical asking prices fall in the range of $30-200 depending on specimen size and radioactivity levels. Quality, size, and provenance can move individual specimens well outside that range.

Is weeksite safe to handle?+

This mineral is radioactive. It contains toxic constituents. Contains uranium; radioactive and chemically toxic if ingested or inhaled as dust. Handle with care, wear gloves, and store in a sealed container away from living areas. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like weeksite?+

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

What minerals are found with weeksite?+

Weeksite commonly co-occurs with Fluorite, Quartz, Chalcedony, Autunite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does weeksite form in?+

Weeksite typically forms in rhyolitic volcanic rocks, hydrothermal veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is weeksite used for?+

Weeksite is used in collector, scientific research.

Find weeksite on the map

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