This substance, which seems almost new to the whole mineralogical world, not being spoken of by any author, was sent me in 1804. It was said to be found in a mine in St. Justs in Cornwall. I speak of it as new, being really a white Schorl or Tourmaline; for though Tourmaline is said to occur of all colours included in mixtures of yellow, red and blue, yet it is not mentioned as ever having been found colourless or white until now; therefore this is the rarest known. It is transparent in the fragments, but is so divided by cracks and flaws in general as to appear of an opaque whiteness in parts. The form of the Crystals agrees with that of Schorl. Their position, lying exposed among Quartz Crystals, is rather new, as Tourmaline mostly occurs imbedded in Ouartz and Petuntse or Feldspar.
The late Hon. Charles Greville, who is much to be lamented from a loss I particularly sustain in the intimate recourse he allowed me to his specimens, pointed out the idea of my specimen being a white Schorl at the time I first showed it to him; even that recollection adds value to the specimen by putting me in mind of a valuable friend, I never could procure a second specimen, or he would have possessed it. I do not know that he ever procured any. I believe Mr. Herbert, who kindly presented me with this, has one also.
Among the small Crystals on this specimen is one that most happily shows the primitive on its end almost detached, as if it were clone on purpose, nearly as figured in the outline, which gives it the appearance of lying fitted on the column; indeed the two acute ends are partly truncated by the narrower faces of the octagonal column.
The right hand outline shows the faces of the pyramid and column, which are very distinct.
The left hand figure represents the modifications of some of the other small Crystals, with three oblique faces not before observed by any author,—the thin outline and shining part shows one of them: it was done thus, in order that it might be known most distinctly.