Downeyite is an extremely rare selenium oxide mineral that forms as a sublimate in areas of coal seam fires. It is typically found as fragile, needle-like acicular crystals or thin crusts associated with burning coal waste environments.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Downeyite

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this downeyite?

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 downeyite with a known reference. Downeyite 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. Downeyite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Downeyite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: yellow, white, colorless.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: acicular crystals, crusts.

Often confused with

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

mineral

Sulfur

Mohs 1.5-2.5

How to tell apart: Luster reads vitreous on Downeyite and resinous on Sulfur.

Compare →

Often found alongside downeyite

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

Sulfur
mineral · Mohs 1.5-2.5

All properties

Chemical formula: SeO₂
Mohs hardness: 2
Density: 5.4 g/cm³
Colors: Yellow White Colorless
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Acicular Crystals, Crusts
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Coal Seam Fire Zones
Typical price: $100-500 for micro-specimens

Where rockhounds find downeyite

Classic worldwide localities

Burning Mountain, New South Wales, Australia

Field-hunting tip

Look in coal seam fire zones country — that is the host setting where downeyite typically forms. If you start seeing sulfur, sal-ammoniac, selen-sulfur in float, you are in the right ground. Field specimens usually show a acicular crystals, crusts habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify downeyite?+

Mohs hardness is 2. It typically shows a vitreous luster. The streak is white. Common colors include yellow, white, colorless.

Where is downeyite found?+

Notable localities include Burning Mountain, New South Wales, Australia.

How much is downeyite worth?+

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

Is downeyite safe to handle?+

It contains toxic constituents. Contains selenium which is toxic if ingested or inhaled as dust; handle with care and wash hands after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like downeyite?+

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

What minerals are found with downeyite?+

Downeyite commonly co-occurs with sulfur, sal-ammoniac, selen-sulfur. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does downeyite form in?+

Downeyite typically forms in coal seam fire zones. Working float back to the host body is the standard way to chase a fresh occurrence.

What is downeyite used for?+

Downeyite is used in collector.

Find downeyite on the map

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