Chessexite is an extremely rare sulfate-bearing silicate mineral primarily known from the alkaline igneous complex at Mont Saint-Hilaire. It typically forms small, colorless to white tabular crystals in cavities of intrusive rocks, often requiring micro-mineral identification techniques for accurate confirmation.

Hardness

Mohs

Luster

Silky

Streak

White

Transparency

Semitransparent

mineralrare

Chessexite

Hardness: 2
Luster: Silky
Streak: White
Transparency: Semitransparent

No image

Is this chessexite?

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 chessexite with a known reference. Chessexite 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: silky.
4
Match the color range
Compare against the expected color range: white.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: microscopic crystals, platy.

Often confused with

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

mineral

Phillipsite

Mohs 4-5

How to tell apart: Phillipsite is the harder of the two (Mohs 4-5 vs. 2); luster reads silky on Chessexite and vitreous on Phillipsite.

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Often found alongside chessexite

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

All properties

Chemical formula: Na₄Ca₂Mg₃Al₈(SiO₄)₂(SO₄)₁₀(OH)₁₀·40H₂O
Mohs hardness: 2
Density: 2.21 g/cm³
Colors: White
Streak: White
Luster: Silky
Transparency: Semitransparent
Crystal system: Orthorhombic
Crystal habit: Microscopic crystals, platy
Cleavage: Indistinct
Rarity: Rare
Uses: Collector
Host rock: As a coating on fluorite

Where rockhounds find chessexite

Classic worldwide localities

Maine fluorite mine, near Autun, Saône-et-Loire, France

Field-hunting tip

Where it forms: As a coating on fluorite. If you start seeing fluorite, gypsum in float, you are in the right ground. Typical habit: microscopic crystals, platy. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify chessexite?+

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

Where is chessexite found?+

Notable localities include Maine fluorite mine, near Autun, Saône-et-Loire, France.

What rocks look like chessexite?+

Chessexite is most often confused with Phillipsite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with chessexite?+

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

What kind of rock does chessexite form in?+

Where it forms: As a coating on fluorite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is chessexite used for?+

Chessexite is used in collector.

Find chessexite on the map

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