Jáchymovite is a rare secondary uranium sulfate mineral discovered in the historic mines of Jáchymov. It typically occurs as delicate, bright yellow crystalline crusts or aggregates associated with other uranium minerals in oxidized zones.

Hardness

2-3

Mohs

Luster

Vitreous

Streak

Pale yellow

Transparency

Translucent

mineralrare

Jáchymovite

Hardness: 2-3
Luster: Vitreous
Streak: Pale yellow
Transparency: Translucent

No image

Is this jáchymovite?

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

Often confused with

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

mineral

Uranopilite

Mohs 2.5

How to tell apart: Luster reads vitreous on Jáchymovite and silky on Uranopilite.

How to tell apart: Streak differs, so Jáchymovite leaves pale yellow, Zippeite leaves yellow white.

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Often found alongside jáchymovite

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

All properties

Chemical formula: (UO₂)₈(SO₄)(OH)₁₄·~13H₂O
Mohs hardness: 2-3
Density: 4.79 g/cm³
Colors: Yellow
Streak: Pale yellow
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Acicular
Cleavage: On {010}, very good
Fluorescence: Bright yellow-green under UV
Rarity: Rare
Uses: Collector
Host rock: Found on a museum specimen from the heavily oxidized portions of a uraninite-bearing vein in dolomite

Where rockhounds find jáchymovite

Classic worldwide localities

Jáchymov (Joachimsthal), Czech Republic

Field-hunting tip

Where it forms: Found on a museum specimen from the heavily oxidized portions of a uraninite-bearing vein in dolomite. If you start seeing gypsum, uranopilite, uraninite in float, you are in the right ground. Typical habit: acicular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify jáchymovite?+

Mohs hardness is 2-3. Luster: vitreous. The streak is pale yellow. Common colors include yellow.

Where is jáchymovite found?+

Notable localities include Jáchymov (Joachimsthal), Czech Republic.

Is jáchymovite safe to handle?+

Jáchymovite contains uranium or thorium and calls for real care. This mineral is radioactive and contains uranium; handle with care using gloves, avoid inhalation of dust, and store in a sealed container away from living spaces.

What rocks look like jáchymovite?+

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

What minerals are found with jáchymovite?+

Jáchymovite commonly co-occurs with Gypsum, Uranopilite, Uraninite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does jáchymovite form in?+

Where it forms: Found on a museum specimen from the heavily oxidized portions of a uraninite-bearing vein in dolomite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is jáchymovite used for?+

Jáchymovite is used in collector.

Find jáchymovite on the map

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