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Cassiterite
Cassiterite is oxide (tin), SnO₂. In the hand, it rates 6 to 7 on the Mohs scale, and it runs black and red-brown. Glossy brown-black crystals with diamond-bright faces and a heft that shocks, tin makes it nearly twice as dense as garnet. Granite-related veins and placers; notable: Bolivia, China, Cornwall (England, historic), Rwanda/DR Congo.
The geology.
Cassiterite carries the formula SnO₂. It belongs to the tetragonal system. On paper it is oxide (tin).
It sits at 6 to 7 on the Mohs scale. The surface reads adamantine to submetallic. Light behaviour is transparent to opaque. Specific gravity runs 6.8 to 7.1. The streak is white to brownish. It breaks with indistinct cleavage; subconchoidal fracture.
Glossy brown-black crystals with diamond-bright faces and a heft that shocks, tin makes it nearly twice as dense as garnet.
Expect to see it as stubby twinned crystals with elbow bends, waterworn pebbles or massive ore.
The origins.
Granite-related veins and placers; notable: Bolivia, China, Cornwall (England, historic), Rwanda/DR Congo.
On value, the database notes: affordable ore pieces; gemmy Bolivian crystals are collector prizes.
Traditional associations.
In energy work traditions, cassiterite has little established lore; some modern writers link it with manifestation and resolve.
Recorded here because it is part of how this material is sold, not because it is a property of the material.
Spotting the real thing.
Glossy brown-black crystals with diamond-bright faces and a heft that shocks, tin makes it nearly twice as dense as garnet.
| Looks like | How to tell them apart |
|---|---|
| Black tourmaline | Schorl feels featherweight beside cassiterite and shows striated prisms |
| Sphalerite | Sphalerite is softer with resinous luster and yellow-brown streak |
| Rutile | Rutile is reddish with lower density (4.2 vs 7) |
At-home tests.
None of these need a lab. A 10x loupe, good daylight and a steady hand cover most of what a buyer needs to know about cassiterite.
| Test | What you should see |
|---|---|
| By weight | Extreme heft (SG ~7) |
| By eye | Adamantine sparkle on crystal faces |
| Scratch check | Scratches glass; pale streak despite dark color |
| By eye | Elbow-shaped twins are classic |
Destructive tests belong to a gemologist, not a kitchen table. If a piece matters to you, pay for an appraisal before you take a file to it.
Care & handling.
At 6 to 7 on the Mohs scale it handles careful wear but scratches against quartz and dust. Store it separately and take rings off before rough work.
It breaks with indistinct cleavage; subconchoidal fracture, which is worth knowing before you set it or drop it.
Clean it by hand, dry it properly, and keep it away from ultrasonic cleaners and hot steam.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is SnO₂. Crystal system: Tetragonal. Specific gravity: 6.8 to 7.1. Streak: White to brownish. Cleavage and fracture: Indistinct cleavage; subconchoidal fracture.
How it reaches the market
Granite-related veins and placers; notable: Bolivia, China, Cornwall (England, historic), Rwanda/DR Congo.
What it gets confused with
Black tourmaline: Schorl feels featherweight beside cassiterite and shows striated prisms. Sphalerite: Sphalerite is softer with resinous luster and yellow-brown streak. Rutile: Rutile is reddish with lower density (4.2 vs 7).
What it is worth
Affordable ore pieces; gemmy Bolivian crystals are collector prizes.
One more thing
Bronze Age civilization ran on cassiterite, Cornish tin traveled the ancient world to be alloyed with copper into bronze.
An education-first guide.
We do not stock cassiterite. Writing it up regardless is the point of a reference library.
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