Meionite

Mount Somma, by Vesuvius in Italy, that produces the Sommite, Tab. VIII, produces also this substance. I am favoured with the use of the specimen now figured by the Count de Bournon, whose scientific collection it enriches. The crystals are prettily relieved by the green chlorite, or talc, ill an hollow or crack of a mixed grey limestone.^* The specimen had apparently been among stones on the sea shore, and had small marine plants on if. The Meionite is crystallized in several varieties, as figured in the outlines at the bottom of the plate. The right-hand figure is a simple rectangular prism, two of whose sides are much enlarged, terminated by four lateral planes or faces, forming a pyramid placed upon its angles. The next figure shows one of the faces enlarged at the expense of the other; the vertical edges of the diminished prism are truncated, giving two of the faces six angles. The left-hand figure shows small faces between the pyramid and the prism; the faces of the pyramid meet each other at an angle of 136°. 20′. hence the pyramid is more obtuse, and consequently the nucleus is shorter than in crystals of such substances as have been confounded with it. From this circumstance it is named by Haüy.

It fractures, according to Haüy, into a rectangular prism with a rectangular base, which is of course the primitive.

The crystals are seldom larger than in the specimen, and are rather confusedly grouped; the cross fracture somewhat conchoidal; it scraches glass, and yields a spongy white glass by means of the blow-pipe.