Giorgiosite is a rare magnesium carbonate mineral that typically forms as soft, chalky white crusts or powdery aggregates. It is primarily found in volcanic fumarolic environments and is structurally related to the hydromagnesite group. Collectors should look for fine-grained white coatings on volcanic rock surfaces.
Is this giorgiosite?
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 giorgiosite with a known reference. Giorgiosite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: silky.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: encrustations, fibrous, spherical.
Often confused with
Giorgiosite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Hydromagnesite is the harder of the two (Mohs 3.5 vs. 2); luster reads silky on Giorgiosite and vitreous; silky to pearly to dull in aggregates on Hydromagnesite.
How to tell apart: Magnesite is the harder of the two (Mohs 3.5-4.5 vs. 2); luster reads silky on Giorgiosite and vitreous on Magnesite.
Often found alongside giorgiosite
Minerals reported to co-occur with giorgiosite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₅(CO₃)₄(OH)₂·5H₂O
- Mohs hardness
- 2
- Density
- 2.155-2.185 g/cm³
- Colors
- Streak
- White
- Luster
- Silky
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Encrustations, fibrous, spherical
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare incrustation on recent lava (Thíra Island, Greece); a weathering product in fractures in sideritic iron formation (Big Fish River-Rapid Creek area, Canada)
Where rockhounds find giorgiosite
Classic worldwide localities
- Alphroëssa, Thíra (Santorini) Island, Cyclades, Greece
- Big Fish River-Rapid Creek area, Yukon Territory, Canada
Field-hunting tip
Where it forms: A rare incrustation on recent lava (Thíra Island, Greece); a weathering product in fractures in sideritic iron formation (Big Fish River-Rapid Creek area, Canada). If you start seeing sodium chloride, sodium sulfate, magnesium carbonate in float, you are in the right ground. Typical habit: encrustations, fibrous, spherical. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify giorgiosite?+
Where is giorgiosite found?+
What rocks look like giorgiosite?+
What minerals are found with giorgiosite?+
What kind of rock does giorgiosite form in?+
What is giorgiosite used for?+
Find giorgiosite on the map
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