Dodecahedral hyaline quartz is frequently found among the vein atones of the lead mines at Beer-alston in Devonshire.
Swimming quartz is met with in the copper mine of Huel Gorland, and in that of Suit and Cloak, or Pednandrae, united with tin and chalcedony. The same quartz is said to be met with at Nancothan.
Compact quartz, passing to quartz-agate and chalcedony, is very common in the old mines of Beer-alston. It may be said to form the principal part of the vein-stones. It is combined with fluor, galena, and blende, which are disseminated through it in small masses.
Calcedony, in the form of stalactites, is found at Huel Sparnan and Trevascus. In the former place, it is combined with chlorophane, a variety of fluor, which was thought to be peculiar to Siberia.[1]
In the copper and tin mine of Tol-carn in the parish of Gwennap, a kind of flint, commonly known in England by the name of chert, has been found with semi-opal in decomposed granite; and jasper agate has been found in the tin mine called Ding—dong in the parish of Gulvall.
Pitchstone has been met with in the copper mine of Carrarach, one of the consolidated mines.[2]
- ↑ Fluate of lime does not usually enter into the composition of primitive rocks; it is said however, that the violet variety called clorophane is found disseminated in a granitic rock, in eastern Siberia; and Dandrada mentions having seen in Sweden, in the district of Norberg, extensive strata of mica-slate mixed with fluate of lime in compact masses, and with nodules of quartz. Brongniart, Traité Elem. de Minér. tome i. p. 246.
- ↑ In the island of Arran, there are appearances of pitch-stone in the form of veins traversing the granite, but as all veins are of posterior formation to the rocks which they traverse, this cannot be equally old with the granite or other rocks reckoned primitive.
These veins (of pitch-stone) traverse the common argillaceous sandstone in Morven, and are often of a great magnitude. In the island of Mull, it seems to lie between sandstone and basalt, but in Eigg it forms considerable veins traversing basalt. Jameson's Mineralogy of the Scottish Isles. vol. i.
