Magnesiovoltaite is a rare sulfate mineral typically found as a secondary phase in the oxidized zones of ore deposits. It forms distinct, dark-colored cubic or cuboctahedral crystals that are structurally related to the voltaite group. Collectors usually identify it by its specific habit and association with other iron and magnesium sulfate minerals.

Hardness

Mohs

Transparency

Transparent

mineralrareVoltaite Group family

Magnesiovoltaite

Hardness: 2.5
Transparency: Transparent

No image

Is this magnesiovoltaite?

3-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 magnesiovoltaite with a known reference. Magnesiovoltaite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
2
Match the color range
Compare against the expected color range: amber-yellow, brownish yellow, pale yellow, pale greenish yellow, almost colorless.
3
Look at form & habit
Crystal system: cubic. Typical habit: cuboctahedral crystals.

Often confused with

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

Often found alongside magnesiovoltaite

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

All properties

Chemical formula: K₂Mg₅Fe³⁺₃Al(SO₄)₁₂·18H₂O
Mohs hardness: 2.5
Density: 2.51 g/cm³
Colors: Amber-yellowBrownish yellow Pale yellow Pale greenish yellowAlmost colorless
Transparency: Transparent
Crystal system: Cubic
Crystal habit: Cuboctahedral crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In the oxidized zone of a hydrothermal, polymetallic, sulfide vein deposit hosted by volcanic rocks in an arid region

Where rockhounds find magnesiovoltaite

Classic worldwide localities

Alcaparrosa mine, north side of Cerro Alcaparrosa, El Loa province, Antofagasta region, Chile

Field-hunting tip

Where it forms: In the oxidized zone of a hydrothermal, polymetallic, sulfide vein deposit hosted by volcanic rocks in an arid region. If you start seeing alum-, rhomboclase, yavapaiite in float, you are in the right ground. Typical habit: cuboctahedral crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify magnesiovoltaite?+

Mohs hardness is 2.5. Common colors include amber-yellow, brownish yellow, pale yellow, pale greenish yellow.

Where is magnesiovoltaite found?+

Notable localities include Alcaparrosa mine, north side of Cerro Alcaparrosa, El Loa province, Antofagasta region, Chile.

What rocks look like magnesiovoltaite?+

Magnesiovoltaite is most often confused with Voltaite, Copiapite, Jarosite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with magnesiovoltaite?+

Magnesiovoltaite commonly co-occurs with Alum-, Rhomboclase, Yavapaiite, Voltaite, Opal, Pickeringite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does magnesiovoltaite form in?+

Where it forms: In the oxidized zone of a hydrothermal, polymetallic, sulfide vein deposit hosted by volcanic rocks in an arid region. Working float back to the host body is the standard way to chase a fresh occurrence.

What is magnesiovoltaite used for?+

Magnesiovoltaite is used in collector.

Find magnesiovoltaite on the map

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