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, 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.