Horákite is a rare bismuth uranium arsenate, typically greenish yellow to pale yellow. It is an oxidation zone, secondary mineral in vugs in quartz veinlets with relics of tennantite and uraninite. It is associated with phosphuranylite and metatorbernite-metazeunerite. It was first described from Jáchymov (St. Joachimsthal), Czech Republic (most likely from the Geister vein at the Rovnost mine).

Hardness

3.5

Mohs

Luster

Vitreous

Streak

Light Yellow

Transparency

Transparent

mineralrare

Horákite

Hardness: 3.5
Luster: Vitreous
Streak: Light Yellow
Transparency: Transparent

No image

Is this horákite?

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 horákite with a known reference. Horákite sits at Mohs 3.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Horákite leaves a light yellow streak.
3
Read the luster
Hold the specimen under a strong light. Horákite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: greenish yellow, pale yellow.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: prismatic to tabular crystals.

Often confused with

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

mineral

Triplite

Mohs 4-5.5

How to tell apart: Streak differs, so Horákite leaves light yellow, Triplite leaves white.

How to tell apart: Amblygonite is the harder of the two (Mohs 5.5-6 vs. 3.5); streak differs, so Horákite leaves light yellow, Amblygonite leaves white.

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Often found alongside horákite

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

All properties

Chemical formula: (Bi₇O₇OH)[(UO₂)₄(PO₄)₂(AsO₄)₂(OH)₂]·3.5H₂O
Mohs hardness: 3.5
Density: 6.538 g/cm³
Colors: Greenish Yellow Pale Yellow
Streak: Light Yellow
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Prismatic to Tabular Crystals
Cleavage: Perfect On {100}
Rarity: Rare
Uses: Collector
Host rock: Granite Pegmatites

Where rockhounds find horákite

Classic worldwide localities

Czech Republic (Otov pegmatite)

Field-hunting tip

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

Common questions

How do you identify horákite?+

Mohs hardness is 3.5. It typically shows a vitreous luster. The streak is light yellow. Common colors include greenish yellow, pale yellow.

Where is horákite found?+

Notable localities include Czech Republic (Otov pegmatite).

Is horákite safe to handle?+

This mineral is radioactive. It contains toxic constituents. Contains arsenic, which is toxic if ingested or inhaled as dust. Contains uranium and is radioactive; store it apart from other specimens. Wash hands thoroughly after handling and avoid creating dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like horákite?+

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

What minerals are found with horákite?+

Horákite commonly co-occurs with Triplite, Fluorapatite, Quartz, Albite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does horákite form in?+

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

What is horákite used for?+

Horákite is used in collector.

Find horákite on the map

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