Abstract

Thermal metamorphism of bituminous limestone to white marble by hot solutions flowing along bedding planes in the original rock is not generally recognized. Most marble deposits in North America, especially those of Vermont, indicate this to be the most important process in development of " crystalline " marbles.Vermont calcite marble deposits extend along a zone of lower Ordovician sediments outcropping from the northwest corner of the state to the middle of the southern border. Sediments in the extreme north are dense, dark, bituminous limestones which take a high polish; in the central part of the state they are mixed white and gray marble; and in the southern region they are a coarse, compact mass of water-white calcite grains.Coloring agents are removed from the limestone and the carbonates recrystallized for variable distances out from bands of chlorite, actinolite, and mica, which mark channels followed by hot solutions. Minor structures closed off parts of folded beds and prevented upward flow of hot solutions locally; these parts of a bed remain almost unmetamorphosed even below highly changed stone. Silicate bands remain as dolomite beds where quarrying operations follow the deposits down into structures which isolated the rock from hot solutions.Most problems of marble as a building material are linked to this peculiar metamorphic origin.

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