Edwardsite is a rare copper cadmium sulfate that forms pale blue tabular to bladed crystals. It is a secondary mineral in the oxidized portion of a Ag-Pb-Zn metal deposit. It is associated with niedermayrite and christelite. It was first described from Block 14 Opencut, Broken Hill, New South Wales, Australia.

Hardness

3-3.5

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrare

Edwardsite

Hardness: 3-3.5
Luster: Vitreous
Streak: White
Transparency: Transparent

No image

Is this edwardsite?

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 edwardsite with a known reference. Edwardsite sits at Mohs 3-3.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: white.
3
Read the luster
Hold the specimen under a strong light. Luster: vitreous.
4
Match the color range
Compare against the expected color range: pale blue.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular to bladed crystals.

Often confused with

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

mineral

Monazite

Mohs 5-5.5

How to tell apart: Monazite is the harder of the two (Mohs 5-5.5 vs. 3-3.5); luster reads vitreous on Edwardsite and resinous on Monazite.

Compare →

Often found alongside edwardsite

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

All properties

Chemical formula: Cu₃Cd₂(SO₄)₂(OH)₆·4H₂O
Mohs hardness: 3-3.5
Density: 3.53 g/cm³
Colors: Pale blue
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Monoclinic
Crystal habit: Tabular to bladed crystals
Cleavage: Excellent on {100}
Rarity: Rare
Uses: Collector
Host rock: A secondary mineral in the oxidized portion of a Ag-Pb-Zn metal deposit

Where rockhounds find edwardsite

Classic worldwide localities

Block 14 Opencut, Broken Hill, New South Wales, Australia

Field-hunting tip

Where it forms: A secondary mineral in the oxidized portion of a Ag-Pb-Zn metal deposit. If you start seeing niedermayrite, christelite in float, you are in the right ground. Typical habit: tabular to bladed crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify edwardsite?+

Mohs hardness is 3-3.5. Luster: vitreous. The streak is white. Common colors include pale blue.

Where is edwardsite found?+

Notable localities include Block 14 Opencut, Broken Hill, New South Wales, Australia.

Is edwardsite safe to handle?+

Edwardsite contains cadmium and copper and calls for real care. Contains cadmium, which is toxic if ingested or inhaled as dust. Wash hands thoroughly after handling and avoid creating dust.

What rocks look like edwardsite?+

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

What minerals are found with edwardsite?+

Edwardsite commonly co-occurs with Niedermayrite, Christelite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does edwardsite form in?+

Where it forms: A secondary mineral in the oxidized portion of a Ag-Pb-Zn metal deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is edwardsite used for?+

Edwardsite is used in collector.

Find edwardsite on the map

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