Since my former communication to the Mineralogical Society I have been endeavouring to obtain a sufficient quantity of the pure mineral therein described to complete my analyses. Plenty of what certain dealers have been selling as Penwithite is obtainable from the rubbish heaps at Wheal Owles, but this is mostly dark-brown—nearly or quite opaque, pitch—like in appearance, and of very variable composition-the silica alone varying from 22 up to 57 p. c., and the sp. gr. often being as high as 3.4.

The true mineral is sometimes attached to masses of such material—it is highly vitreous and transparent, from dark amber to reddish-brown in colour, H. 3.5 and sp. gr. only 2.49—a remarkable circumstance considering the large amount of manganous oxide present.