Alpersite is a rare magnesium-dominant sulfate mineral that typically forms as efflorescent crusts or fibrous aggregates in mine environments. It is most commonly found as a secondary mineral resulting from the oxidation of sulfide ores, particularly in sites affected by acid mine drainage.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrareMelanterite Group family

Alpersite

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

Is this alpersite?

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 alpersite with a known reference. Alpersite 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. Alpersite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Alpersite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: blue, blue-green.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: fibrous, crystalline crusts.

Often confused with

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

Often found alongside alpersite

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

All properties

Chemical formula: (Mg,Cu)SO₄·7H₂O
Mohs hardness: 2
Density: 1.97 g/cm³
Colors: Blue Blue-green
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Fibrous, Crystalline Crusts
Cleavage: Perfect On {001}
Rarity: Rare
Uses: Collector
Host rock: Acid Mine Drainage Environments, Weathered Sulfide Deposits
Typical price: $20-100 for small specimens

Where rockhounds find alpersite

Classic worldwide localities

Iron Mountain Mine, California, USA
Rio Tinto, Spain

Field-hunting tip

Look in acid mine drainage environments, weathered sulfide deposits country — that is the host setting where alpersite typically forms. If you start seeing melanterite, goslarite, chalcanthite in float, you are in the right ground. Field specimens usually show a fibrous, crystalline crusts habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify alpersite?+

Mohs hardness is 2. It typically shows a vitreous luster. The streak is white. Common colors include blue, blue-green.

Where is alpersite found?+

Notable localities include Iron Mountain Mine, California, USA; Rio Tinto, Spain.

How much is alpersite worth?+

Typical asking prices fall in the range of $20-100 for small specimens. Quality, size, and provenance can move individual specimens well outside that range.

Is alpersite safe to handle?+

It contains toxic constituents. Contains copper and sulfates; avoid ingestion or inhalation of dust. Wash hands thoroughly after handling as it is highly water-soluble. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like alpersite?+

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

What minerals are found with alpersite?+

Alpersite commonly co-occurs with Melanterite, Goslarite, Chalcanthite, Copiapite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does alpersite form in?+

Alpersite typically forms in acid mine drainage environments, weathered sulfide deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is alpersite used for?+

Alpersite is used in collector.

Find alpersite on the map

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