Holfertite is a very rare uranyl titanate mineral found primarily in rhyolite gas cavities. It is most commonly identified by its distinctive radiating clusters of yellow needles that grow in association with topaz and bixbyite.

Hardness

Mohs

Luster

Adamantine

Streak

Pale yellow

Transparency

Transparent to translucent

mineralrare

Holfertite

Hardness: 4
Luster: Adamantine
Streak: Pale yellow
Transparency: Transparent to translucent

Is this holfertite?

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 holfertite with a known reference. Holfertite sits at Mohs 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: pale yellow.
3
Read the luster
Hold the specimen under a strong light. Luster: adamantine.
4
Match the color range
Compare against the expected color range: canary yellow, orange yellow.
5
Look at form & habit
Crystal system: trigonal. Typical habit: acicular.

Often confused with

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

mineral

Uranophane

Mohs 2.5

How to tell apart: Holfertite is noticeably harder (Mohs 4 vs. 2.5); streak differs, so Holfertite leaves pale yellow, Uranophane leaves yellowish white; luster reads adamantine on Holfertite and vitreous on Uranophane.

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Often found alongside holfertite

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

All properties

Chemical formula: (UO₂)₁.₇₅Ca₀.₂₅TiO₄·3H₂O
Mohs hardness: 4
Density: 4.22-4.26 g/cm³
Colors: Canary yellow Orange yellow
Streak: Pale yellow
Luster: Adamantine
Transparency: Transparent to translucent
Crystal system: Trigonal
Crystal habit: Acicular
Cleavage: Perfect on {110}
Rarity: Rare
Uses: Collector
Host rock: A pneumatolytic phase in rhyolite

Where rockhounds find holfertite

Classic worldwide localities

Starvation (formerly Searle) Canyon, Thomas Range, Utah, USA

Field-hunting tip

Where it forms: A pneumatolytic phase in rhyolite. If you start seeing hematite, bixbyite, fluorite 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 holfertite?+

Mohs hardness is 4. Luster: adamantine. The streak is pale yellow. Common colors include canary yellow, orange yellow.

Where is holfertite found?+

Notable localities include Starvation (formerly Searle) Canyon, Thomas Range, Utah, USA.

Is holfertite safe to handle?+

Holfertite contains uranium or thorium and calls for real care. Contains uranium; handle with care, wash hands thoroughly after handling, and store in a shielded container to minimize exposure to radiation.

What rocks look like holfertite?+

Holfertite is most often confused with Uranophane. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with holfertite?+

Holfertite commonly co-occurs with Hematite, Bixbyite, Fluorite, Topaz, Beryl, Calcite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does holfertite form in?+

Where it forms: A pneumatolytic phase in rhyolite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is holfertite used for?+

Holfertite is used in collector.

Find holfertite on the map

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