Cassiterite
Tin oxide (SnO2)
Tin oxide and the principal ore of tin, a dense, hard mineral mined since the Bronze Age for tin metal.
- Mohs hardness
- 6-7
- Color
- Brown to black, sometimes yellow or red
- Type
- mineral
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Overview
Cassiterite is tin oxide (SnO2) and the most important ore of tin. It is usually brown to black, with an adamantine to greasy luster, and is notably dense and hard for an ore mineral.
Cassiterite has been mined since antiquity, when tin combined with copper produced bronze, defining an entire age of human technology. It forms well-shaped crystals as well as rounded grains and fibrous botryoidal masses called wood tin.
Because it is heavy and resistant to weathering, cassiterite concentrates in stream gravels as stream tin, historically recovered by simple panning and sluicing.
Formation & geology
Cassiterite forms mainly in high-temperature hydrothermal veins and in granitic pegmatites and greisens associated with tin-bearing granite intrusions. Hot, tin-rich fluids deposit it along with minerals such as quartz, topaz, tourmaline, and wolframite.
Because cassiterite is dense and chemically durable, weathering of these primary deposits releases grains that accumulate in placer (stream tin) deposits, which have historically supplied much of the world's tin.
Major producing regions include Southeast Asia (Malaysia, Indonesia, Myanmar), China, Bolivia, Africa, and the historic tin districts of Cornwall in England.
How to identify it
Cassiterite is identified by its high density (it feels very heavy), hardness of 6-7, adamantine to greasy luster, and brown to black color. Its streak is white to pale brown, lighter than the mineral itself, a useful diagnostic.
The great heaviness combined with high hardness distinguishes cassiterite from other dark heavy minerals like hematite (red-brown streak, softer) and from rutile. Wood tin shows fibrous, banded, rounded masses.
Well-formed crystals are often short prisms with pyramid terminations, sometimes twinned. The pale streak despite a dark body color and the unusual combination of high hardness and high density are key identifiers.
Uses & significance
Cassiterite is the world's primary ore of tin, refined to produce tin for solder, tinplate (coating steel cans), bronze and pewter alloys, and many chemical and electronic applications.
Its use stretches back to the Bronze Age, when tin from cassiterite was alloyed with copper to make bronze. Today tin remains vital in electronics, especially in lead-free solder.
Well-crystallized cassiterite, including gem-quality transparent material, is valued by mineral and gem collectors, though its main importance is industrial.
Frequently asked questions
What is cassiterite used for?
It is the main ore of tin, refined to make solder, tinplate for cans, bronze and pewter alloys, and electronic components.
How do I identify cassiterite?
Look for a very heavy, hard (6-7), brown-to-black mineral with adamantine luster and a pale white-to-brown streak despite its dark color.
What is wood tin?
Wood tin is a fibrous, banded, rounded form of cassiterite that superficially resembles wood grain.
Why was cassiterite important historically?
Tin smelted from cassiterite was alloyed with copper to make bronze, giving rise to the Bronze Age and early metal tools and weapons.
Cassiterite guides
In-depth guides for identifying, valuing, and understanding Cassiterite.
