Feodosiyite is a rare copper chloride mineral discovered in the volcanic fumaroles of the Tolbachik volcano in Kamchatka, Russia. It typically forms delicate white platy crystals and is highly sensitive to atmospheric moisture, making it a challenging and rare acquisition for specialized mineral collectors.
Is this feodosiyite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch feodosiyite with a known reference. Feodosiyite sits at Mohs 1.5-2 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Feodosiyite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Feodosiyite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy crystals.
Often confused with
Feodosiyite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Atacamite is the harder of the two (Mohs 3-3.5 vs. 1.5-2); streak differs — Feodosiyite leaves white, Atacamite leaves apple green; luster reads pearly on Feodosiyite and adamantine to vitreous on Atacamite.
How to tell apart: Paratacamite is the harder of the two (Mohs 3 vs. 1.5-2); streak differs — Feodosiyite leaves white, Paratacamite leaves apple green; luster reads pearly on Feodosiyite and adamantine on Paratacamite.
How to tell apart: Clinoatacamite is the harder of the two (Mohs 3 vs. 1.5-2); streak differs — Feodosiyite leaves white, Clinoatacamite leaves apple green; luster reads pearly on Feodosiyite and vitreous on Clinoatacamite.
Often found alongside feodosiyite
Minerals reported to co-occur with feodosiyite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₄Cl₂(OH)₆
- Mohs hardness
- 1.5-2
- Density
- 3.5 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy Crystals
- Cleavage
- Perfect On {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Volcanic Fumaroles
- Typical price
- n/a
Where rockhounds find feodosiyite
Classic worldwide localities
- Tolbachik volcano, Kamchatka, Russia
Field-hunting tip
Look in volcanic fumaroles country — that is the host setting where feodosiyite typically forms. If you start seeing tenorite, sylvite, halite in float, you are in the right ground. Field specimens usually show a platy crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify feodosiyite?+
Where is feodosiyite found?+
How much is feodosiyite worth?+
Is feodosiyite safe to handle?+
What rocks look like feodosiyite?+
What minerals are found with feodosiyite?+
What kind of rock does feodosiyite form in?+
What is feodosiyite used for?+
Find feodosiyite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
