For the commoner grades of dark-coloured bottles the glass mixture is cheapened by substituting common salt for part of the sulphate of soda, and by the addition of felspar, granite, granulite, furnace slag and other substances fusible at a high temperature.
Glass is made from granulite found in the Meldon Valley, 3 m.
Graphite occurs mainly in the older crystalline rocks - gneiss, granulite, schist and crystalline limestone - and also sometimes in granite: it is found as isolated scales embedded in these rocks, or as large irregular masses or filling veins.
The granulite, also called eurite and halleflinta, is the most important of the Pre-Cambrian formation, as it contains all the metalliferous deposits of Sweden.
The metalliferous deposits have generally the form of beds or layers between the strata of granulite and limestone.