Maxwellite is an extremely rare arsenic-bearing mineral found primarily in the Thomas Range of Utah. It typically occurs as small, bladed crystals within gas cavities of rhyolite flows, frequently associated with other rare topaz-related minerals.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrarenull family

Maxwellite

Hardness: 4
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this maxwellite?

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 maxwellite with a known reference. Maxwellite 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. Maxwellite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Maxwellite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: white, colorless, yellowish.
5
Look at form & habit
Crystal system: triclinic. Typical habit: bladed crystals.

Often confused with

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

mineral

Tilasite

Mohs 5

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

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

Compare →

Often found alongside maxwellite

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

All properties

Chemical formula: NaFe³⁺₂(AsO₄)₂F
Mohs hardness: 4
Density: 4.82 g/cm³
Colors: White Colorless Yellowish
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Triclinic
Crystal habit: Bladed Crystals
Cleavage: Perfect in One Direction
Rarity: Rare
Uses: Collector
Host rock: Rhyolite Cavities
Typical price: $100-500 for small thumbnail specimens

Where rockhounds find maxwellite

Classic worldwide localities

Thomas Range, Juab County, Utah, USA

Field-hunting tip

Look in rhyolite cavities country — that is the host setting where maxwellite typically forms. If you start seeing topaz, bixbyite, pseudobrookite in float, you are in the right ground. Field specimens usually show a bladed crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify maxwellite?+

Mohs hardness is 4. It typically shows a vitreous luster. The streak is white. Common colors include white, colorless, yellowish.

Where is maxwellite found?+

Notable localities include Thomas Range, Juab County, Utah, USA.

How much is maxwellite worth?+

Typical asking prices fall in the range of $100-500 for small thumbnail specimens. Quality, size, and provenance can move individual specimens well outside that range.

Is maxwellite safe to handle?+

It contains toxic constituents. Contains arsenic; handle with care and wash hands thoroughly after contact. Do not inhale dust or allow to come into contact with skin or mucous membranes. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like maxwellite?+

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

What minerals are found with maxwellite?+

Maxwellite commonly co-occurs with topaz, bixbyite, pseudobrookite, hematite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does maxwellite form in?+

Maxwellite typically forms in rhyolite cavities. Working float back to the host body is the standard way to chase a fresh occurrence.

What is maxwellite used for?+

Maxwellite is used in collector.

Find maxwellite on the map

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