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Dartmoor Tinworking…. What is tinworking you may ask? Well, it’s the extraction of the mineral Cassiterite a tin oxide (SnO₂). On Mohs mineral hardness scale of 1 to 10, Cassiterite is placed between 6 and 6½ just below Topaz. The scale was created by a German mineralogist called Friedrich Mohs in 1812. The specific gravity of Cassiterite is between 6.8 and 7.1, which makes it very heavy, and easy to separate from the waste material.

Cassiterite is found in many forms like the well-known quartz crystals that have 6 faces, and taper to form a point. This is known as crystalised tin. It also occurs in the following forms, massive, fibrous, disseminated (in small grains), and alluvial. Deposits of alluvial tin can be found in almost every river, stream, or brook on Dartmoor, and is basically water-worn grains or stones that resemble beech pebbles. Varieties of tin include Wood Tin, Toad’s Eye Tin and Stream Tin.

Wood Tin internally has a compact and fibrous structure, and occurs in reniform masses (Kidney shaped). Whereas Toad’s Eye Tin resembles very similar characteristics as Wood Tin, but on a much smaller scale. Stream Tin results from the wearing-away of tin veins in the country (host rock) and eventually finds its way into the rivers, streams and brooks. The tin sinks to the bottom of the river beds and forms deposits known as ‘Alluvial’ These deposits accounted for almost all the very early tin sold by the ancient miners. With the stream tin almost exhausted the miners' started following the tin veins into the hillside. This was done by opencast mining, and a number of ancient Beams and Gerts can still be on seen Dartmoor.

At a much later date after the majority of surface tin had been obtained by the miners’ underground mining started. A horizontal level was driven into the hillside at a very slight inclined angle so the water could freely run out of the level. A short while later shaft mining took place connecting a vertical shaft or shafts to the horizontal adit level. Here cross-cuts were driven at right angles to the strike of the lode to search for other mineral veins. The strike of Cassiterite veins generally runs in an east - west direction, and in some cases, either a north-west to south-east, or north-east to south-west which is known as a Caunter lode.

Dartmoor has well over 1,000 recorded early tinworks, and documents relating to them can be found in local record offices. Dr. Tom Greeves who has spent many years studying this subject is probably the leading authority on Dartmoor’s streamworks. His thesis can be found in the local Plymouth Reference Library, and is well worth viewing for any potential researcher.

Eighteenth and nineteenth century tin mining has much more information available through all local libraries, record offices, and even now the internet. A number of well-known researchers have uncovered some very useful information over the years, along with facts and figures of tin sold from Dartmoor’s tin mines.

This website will try to bring as much information as is practicable for the compilers to upload for the DTRG members, and others who have a common interest in Dartmoor’s tin mines.

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