Carboborite is an extremely rare hydrous calcium magnesium carbonate-borate mineral found in borate-rich salt deposits. Collectors typically identify it by its tabular crystal habit and association with other rarer borate minerals in specialized geological environments.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Translucent

mineralrare

Carboborite

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Translucent

No image

Is this carboborite?

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 carboborite with a known reference. Carboborite sits at Mohs 2, 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: colorless.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: tabular crystals.

Often confused with

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

How to tell apart: Colemanite is the harder of the two (Mohs 4.5 vs. 2).

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Often found alongside carboborite

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

All properties

Chemical formula: Ca₂Mg[B(OH)₄]₂(CO₃)₂·4H₂O
Mohs hardness: 2
Density: 2.12 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Tabular crystals
Cleavage: {101}, perfect; {110}, distinct; {001}, imperfect
Fluorescence: White under SW and LW UV
Rarity: Rare
Uses: Collector
Host rock: In a lacustrine borate deposit

Where rockhounds find carboborite

Classic worldwide localities

China, at an unspecified locality [Dafangshan, Qinghai Plateau, Tibet]

Field-hunting tip

Where it forms: In a lacustrine borate deposit. If you start seeing ulexite, hydroboracite, gypsum in float, you are in the right ground. Typical habit: tabular crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify carboborite?+

Mohs hardness is 2. Luster: vitreous. The streak is white. Common colors include colorless.

Where is carboborite found?+

Notable localities include China, at an unspecified locality [Dafangshan, Qinghai Plateau, Tibet].

What rocks look like carboborite?+

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

What minerals are found with carboborite?+

Carboborite commonly co-occurs with Ulexite, Hydroboracite, Gypsum. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does carboborite form in?+

Where it forms: In a lacustrine borate deposit. Working float back to the host body is the standard way to chase a fresh occurrence.

What is carboborite used for?+

Carboborite is used in collector.

Find carboborite on the map

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