Cockle is a historic Cornish mining term for schorl, the black, iron-rich variety of tourmaline. It commonly occurs as long, striated, opaque prismatic crystals in granitic pegmatites and hydrothermal veins. Tin miners often found cockle associated with cassiterite, making it an important indicator mineral, though its high density made it difficult to separate from the valuable tin ore during washing.
The lode here is choked with cockle, but there should be good tin just beyond it.
Because it is heavy and black, novice prospectors sometimes mistake cockle for tin ore itself.
Also heard as
- schorl
- black tourmaline
Related terms
Elvan
A traditional mining term for a dyke of quartz-porphyry or fine-grained granite.
Growan
A highly weathered, crumbly granite found in tin mining districts.
Black tin
Dressed and washed cassiterite ore that is ready for the smelting furnace.
Lode
A defined vein or tabular deposit of valuable metallic ore embedded within barren rock.