The different appearances that various substances assume is the greatest stumbling-block in Mineralogy: it becomes therefore necessary to learn them; and although forms under the same terms may belong to various substances, they are nevertheless often characteristic of particular species. The present variety, although not common, is pretty well known among the Cornish miners, who call it Cockle, which is generally recognised as Schorl or Tourmaline by mineralogists. See tab. 209 and 210. We may find specimens that lead from the more crystallized form of those of the filamentose structure through a great variety of arrangement to the present stellated one, where the crystals shoot as it were from a centre, are thin, and interrupted in their forms by pressing among each other; so that externally we guess at them from a similarity in appearance to those of a more conspicuous size, generally angular, and mostly shining and longitudinally striated on all sides. If experience does not determine them to our satisfaction in this, we must proceed to hardness, electricity, &c., to find their correspondence. Our specimen is rather remarkable, being in a gangue chiefly composed of Mica. I have a specimen from Aberdeen nearly like it; but the Schorl is chiefly imbedded in Quartz, and a mass of Mica attached to the specimen has only a few scattered bits in it.