Stokesite is a rare calcium tin silicate that typically forms as small, colorless, prismatic crystals. It is primarily prized by advanced mineral collectors and is most famously associated with granite pegmatite deposits where it occurs as a secondary mineral in vugs.

Hardness

Mohs

Luster

Vitreous, pearly on {100}

Streak

White

Transparency

Transparent

mineralrare

Stokesite

Hardness: ~6
Luster: Vitreous, pearly on {100}
Streak: White
Transparency: Transparent

Is this stokesite?

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 stokesite with a known reference. Stokesite sits at Mohs ~6, 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, pearly on {100}.
4
Match the color range
Compare against the expected color range: colorless.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: massive.

Often confused with

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

mineral

Apophyllite

Mohs 4-5

How to tell apart: Stokesite is noticeably harder (Mohs ~6 vs. 4-5).

Often found alongside stokesite

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

All properties

Chemical formula: CaSnSi₃O₉·2H₂O
Mohs hardness: ~6
Density: 3.185 g/cm³
Colors: Colorless
Streak: White
Luster: Vitreous, pearly on {100}
Transparency: Transparent
Crystal system: Orthorhombic
Crystal habit: Massive
Cleavage: Perfect on {101}, imperfect on {100}
Rarity: Rare
Uses: Collector
Host rock: On axinite (Roscommon Cli®, England); in miarolitic cavities in a quartz-albite pegmatite (Věžná, Czech Republic)

Where rockhounds find stokesite

Classic worldwide localities

Himalaya mine, Mesa Grande district, San Diego Co., California, USA
Roscommon Cli®, St. Just, and in the Halvosso quarry, Longdowns, Cornwall, England
Ctidružice and Věžná, Czech Republic
Pitkäranta district, Lake Lagoda, Karelia
Crystals from Corrégo do Urucum, near Galiléia, Minas Gerais, Brazil
Iwaguro Sekizai quarry, Tahara, Gifu Prefecture, Japan

Field-hunting tip

Where it forms: On axinite (Roscommon Cli®, England); in miarolitic cavities in a quartz-albite pegmatite (Věžná, Czech Republic). If you start seeing axinite, cassiterite, albite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify stokesite?+

Mohs hardness is ~6. Luster: vitreous, pearly on {100}. The streak is white. Common colors include colorless.

Where is stokesite found?+

Notable localities include Himalaya mine, Mesa Grande district, San Diego Co., California, USA; Roscommon Cli®, St. Just, and in the Halvosso quarry, Longdowns, Cornwall, England; Ctidružice and Věžná, Czech Republic; Pitkäranta district, Lake Lagoda, Karelia; Crystals from Corrégo do Urucum, near Galiléia, Minas Gerais, Brazil.

What rocks look like stokesite?+

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

What minerals are found with stokesite?+

Stokesite commonly co-occurs with Axinite, Cassiterite, Albite, Titanite, Beryl, Microlite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does stokesite form in?+

Where it forms: On axinite (Roscommon Cli®, England); in miarolitic cavities in a quartz-albite pegmatite (Věžná, Czech Republic). Working float back to the host body is the standard way to chase a fresh occurrence.

What is stokesite used for?+

Stokesite is used in collector.

Find stokesite on the map

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