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Magnesiocopiapite is a secondary sulfate mineral that typically forms as an efflorescent crust or thin coating in the weathering zones of sulfide deposits. It is best identified by its bright yellow color and occurrence alongside other iron-sulfates; it is highly water-soluble and should be kept dry.

Hardness
2.5-3
Mohs
Luster
Pearly
Streak
Light yellow
Transparency
Semitransparent

Is this magnesiocopiapite?

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 magnesiocopiapite with a known reference. Magnesiocopiapite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: light yellow.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: pearly.
  • 4
    Match the color range
    Compare against the expected color range: yellow, green yellow, yellow green, orange.
  • 5
    Look at form & habit
    Crystal system: triclinic. Typical habit: platy crystals, granular crusts, efflorescent aggregates.

Often confused with

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

Copiapite mineral
mineral
Copiapite
Mohs 2.5-3

How to tell apart: Streak differs, so Magnesiocopiapite leaves light yellow, Copiapite leaves pale yellow.

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Fibroferrite mineral
mineral
Fibroferrite
Mohs ~2.5

How to tell apart: Streak differs, so Magnesiocopiapite leaves light yellow, Fibroferrite leaves white.

Compare →

Often found alongside magnesiocopiapite

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

All properties

Chemical formula
MgFe₄³⁺(SO₄)₆(OH)₂·20H₂O
Mohs hardness
2.5-3
Density
2.08-2.17 g/cm³
Colors
YellowGreen yellowYellow greenOrange
Streak
Light yellow
Luster
Pearly
Transparency
Semitransparent
Crystal system
Triclinic
Crystal habit
Platy crystals, granular crusts, efflorescent aggregates
Cleavage
On {010}, perfect (by analogy to copiapite group members)
Rarity
Uncommon
Uses
Collector
Host rock
An uncommon secondary mineral, typically formed by oxidation of pyrite

Where rockhounds find magnesiocopiapite

Classic worldwide localities

  • Blythe, Riverside Co., and at the Redington mercury mine, Knoxville, Napa Co., California, USA
  • Las Vegas, Tecolote district, San Miguel Co., New Mexico, USA
  • Denver mine, Santa Cruz Co., and the United Verde mine, Jerome, Yavapai Co., Arizona, USA
  • A prospect pit along the Mosquito Fork, Forty Mile River, Eagle A-3 quadrangle, Alaska, USA
  • Prince mine, Cape Breton Island, Nova Scotia, Canada
  • Falun, Kopparberg, Sweden

Field-hunting tip

Where it forms: An uncommon secondary mineral, typically formed by oxidation of pyrite. If you start seeing pyrite, römerite, paracoquimbite in float, you are in the right ground. Typical habit: platy crystals, granular crusts, efflorescent aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify magnesiocopiapite?+
Mohs hardness is 2.5-3. Luster: pearly. The streak is light yellow. Common colors include yellow, green yellow, yellow green, orange.
Where is magnesiocopiapite found?+
Notable localities include Blythe, Riverside Co., and at the Redington mercury mine, Knoxville, Napa Co., California, USA; Las Vegas, Tecolote district, San Miguel Co., New Mexico, USA; Denver mine, Santa Cruz Co., and the United Verde mine, Jerome, Yavapai Co., Arizona, USA; A prospect pit along the Mosquito Fork, Forty Mile River, Eagle A-3 quadrangle, Alaska, USA; Prince mine, Cape Breton Island, Nova Scotia, Canada.
What rocks look like magnesiocopiapite?+
Magnesiocopiapite is most often confused with Copiapite, Fibroferrite. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with magnesiocopiapite?+
Magnesiocopiapite commonly co-occurs with Pyrite, Römerite, Paracoquimbite, Halotrichite, Redingtonite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does magnesiocopiapite form in?+
Where it forms: An uncommon secondary mineral, typically formed by oxidation of pyrite. Working float back to the host body is the standard way to chase a fresh occurrence.
What is magnesiocopiapite used for?+
Magnesiocopiapite is used in collector.

Find magnesiocopiapite on the map

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