Monohydrocalcite is an uncommon hydrated calcium carbonate mineral that typically forms in evaporitic environments, alkaline lakes, or occasionally as a cave deposit. It is metastable and often converts to calcite over time if dehydrated, so collectors should store specimens in sealed containers to preserve their integrity.
Is this monohydrocalcite?
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 monohydrocalcite with a known reference. Monohydrocalcite sits at Mohs 2-3, 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: earthy.
- 4Match the color rangeCompare against the expected color range: white, gray, gray white, light blue, light green.
- 5Look at form & habitCrystal system: trigonal. Typical habit: cryptocrystalline, earthy.
Often confused with
Monohydrocalcite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads earthy on Monohydrocalcite and vitreous; pearly on cleavages and {0001} on Calcite.
How to tell apart: Luster reads earthy on Monohydrocalcite and vitreous, resinous on fracture surfaces on Aragonite.
Often found alongside monohydrocalcite
Minerals reported to co-occur with monohydrocalcite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaCO₃·H₂O
- Mohs hardness
- 2-3
- Density
- 2.38 g/cm³
- Streak
- White
- Luster
- Earthy
- Transparency
- Transparent to opaque
- Crystal system
- Trigonal
- Crystal habit
- Cryptocrystalline, earthy
- Cleavage
- Perfect
- Fluorescence
- Vivid green under SW UV; green under LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In lake-bed sediments and as tuffaceous deposits on lake margins, formed by precipitation at pH > 8.0 and high Mg:Ca or by biological activity
Where rockhounds find monohydrocalcite
Classic worldwide localities
- Gunsight, Cottonwood, and Hidden Caves, Guadalupe Mountains, Eddy Co., New Mexico, USA
- Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Lake Issyk-Kol, Kyrgyzstan
- Lakes Maibalyk and Teke, Kazakhstan
- Lake Kivu, on the Congo (Zaire)–Rwanda border
- Sarfartôq carbonatite complex, near Kangerdlugssuaq, Greenland
Field-hunting tip
Where it forms: In lake-bed sediments and as tuffaceous deposits on lake margins, formed by precipitation at pH > 8.0 and high Mg:Ca or by biological activity. If you start seeing calcite, aragonite, hydromagnesite in float, you are in the right ground. Typical habit: cryptocrystalline, earthy. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify monohydrocalcite?+
Where is monohydrocalcite found?+
What rocks look like monohydrocalcite?+
What minerals are found with monohydrocalcite?+
What kind of rock does monohydrocalcite form in?+
What is monohydrocalcite used for?+
Find monohydrocalcite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
