Ch. 4: Quartz in Maine

Ch. 4: Quartz in Maine Page of 170 Ch. 4: Quartz in Maine Text size:minus plus Restore normal size   Mail page  Print this page
134              PEGMATITES AND ASSOCIATED ROCKS OF MAINE.
In the wet process the quartz may be crushed just as it comes from the quarry, or it may first be highly heated in kilns and then fractured by turning upon it a stream of cold water. The first crushing is effected by jaw crushers, or if the quartz has previously been burned it may be crushed in chaser mills. In a few mills the chasers revolve in wet pans and are periodically stopped to allow the crushed quartz to be shoveled out. After crushing, it is ground in "wet pans" pro­vided with a pavement of flat-faced quartz or quartzite blocks over which move several large blocks of similar material, the crushed quartz being pulverized between these blocks and the pavement. The grinding in wet pans usually occupies about twenty-four hours, the load ground in a single pan varying from 1,200 to 1,800 pounds. From the wet pans the pastelike mass of quartz and water is drawn into settling troughs, the first settlings being in some cases returned to the pans for finer grinding. From the settling troughs it is shoveled out upon drying floors heated by steam or hot air, or else it is dried in small pans which are placed tier on tier on heated racks constructed of steam pipes. Finally the dried material is bolted to various degrees of fineness and packed in bags for shipment, or it may be shipped in bulk.
In the dry method of treatment the quartz is usually crushed first in a jaw crusher and then between crushing rolls. Quartz to be used for filters and for abrasive purposes is then screened to various degrees of fineness and is packed in bags for shipment. In the manufacture of the finer grades for use in pottery, wood fillers, scouring soaps, etc., the material after leaving the roll crushers is ground in tube mills, either of the continuous or of the intermittent type. It is then graded to various sizes either by bolting or by a pneumatic process whereby the quartz powder is carried by a strong air current through" a series of tubes and receptacles, the distance to which the quartz is carried being dependent upon its fineness. There are no quartz mills in Maine. Those nearest to that State are in Connecticut.
Uses.—Quartz is used for a great variety of purposes, the principal uses being in the manufacture of wood filler, pottery, paints, and scouring soaps. In pottery the quartz serves to diminish shrinkage in the body of the ware; it is used also in many glazes. Quartz for these purposes should contain in general less than one-half of 1 per cent of iron oxide. Finely ground quartz is used in paints in various proportions up to one-third of the total pigment used. Its chemical inertness prevents it from combining with other constituents of the paint and increases the resistance of the paint to the weather. Crys­talline quartz is superior to silica sand for this purpose because the ground particles are highly angular and tend to attach themselves more firmly to the painted surfaces, thus giving the paint what is known as a "tooth" and after some wear affording a good surface-
Ch. 4: Quartz in Maine Page of 170 Ch. 4: Quartz in Maine
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