Hydroniumpharmacosiderite is a rare secondary mineral typically found in the oxidation zones of arsenic-bearing mineral deposits. It occurs as small, sharp, pseudocubic crystals that closely resemble standard pharmacosiderite but are distinguished primarily through chemical analysis or specialized X-ray diffraction due to the hydronium ion substitution.

Hardness

2-3

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineralrarePharmacosiderite Group family

Hydroniumpharmacosiderite

Hardness: 2-3
Luster: Vitreous
Streak: White
Transparency: Transparent

No image

Is this hydroniumpharmacosiderite?

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 hydroniumpharmacosiderite with a known reference. Hydroniumpharmacosiderite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: 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: yellowish green.
5
Look at form & habit
Crystal system: cubic. Typical habit: pseudocubic crystals, massive, granular.

Often confused with

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

mineral

Pharmacosiderite

Mohs 2.5

How to tell apart: Streak differs, so Hydroniumpharmacosiderite leaves white, Pharmacosiderite leaves yellowish green; luster reads vitreous on Hydroniumpharmacosiderite and adamantine to greasy on Pharmacosiderite.

How to tell apart: Streak differs, so Hydroniumpharmacosiderite leaves white, Scorodite leaves greenish white.

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Often found alongside hydroniumpharmacosiderite

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

All properties

Chemical formula: (H₃O)Fe₄(AsO₄)₃(OH)₄·4H₂O
Mohs hardness: 2-3
Density: 2.559 g/cm³
Colors: Yellowish green
Streak: White
Luster: Vitreous
Transparency: Transparent
Crystal system: Cubic
Crystal habit: Pseudocubic crystals, massive, granular
Cleavage: On {001}. [By analogy with other pharmacosiderite group minerals
Rarity: Rare
Uses: Collector

Where rockhounds find hydroniumpharmacosiderite

Classic worldwide localities

Cornwall, England (probably the St. Day group of mines)
Wendy pit, Tambo mine, Elqui Province, Coquimbo Region, Chile

Field-hunting tip

If you start seeing arsenopyrite, limonite, goethite in float, you are in the right ground. Typical habit: pseudocubic crystals, massive, granular. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify hydroniumpharmacosiderite?+

Mohs hardness is 2-3. Luster: vitreous. The streak is white. Common colors include yellowish green.

Where is hydroniumpharmacosiderite found?+

Notable localities include Cornwall, England (probably the St. Day group of mines); Wendy pit, Tambo mine, Elqui Province, Coquimbo Region, Chile.

Is hydroniumpharmacosiderite safe to handle?+

Hydroniumpharmacosiderite contains arsenic and calls for real care. Contains arsenic, which is toxic if ingested or inhaled as dust. Wash hands thoroughly after handling and avoid creating dust when breaking specimens.

What rocks look like hydroniumpharmacosiderite?+

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

What minerals are found with hydroniumpharmacosiderite?+

Hydroniumpharmacosiderite commonly co-occurs with Arsenopyrite, Limonite, Goethite, Scorodite. Spotting any of these in float or country rock is a useful trip signal.

What is hydroniumpharmacosiderite used for?+

Hydroniumpharmacosiderite is used in collector.

Find hydroniumpharmacosiderite on the map

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