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The geology of Massachusetts includes numerous units of volcanic, intrusive igneous, metamorphic and sedimentary rocks formed within the last 1.2 billion years. The oldest formations are gneiss rocks in the Berkshires , which were metamorphosed from older rocks during the Proterozoic Grenville orogeny as the proto-North American continent ...
Milford pink granite, also known as Milford granite or Milford pink is a Proterozoic igneous rock located in and around the town of Milford, Massachusetts, covering an area of approximately 39 square miles (100 km 2), as mapped by the USGS.
Based on radiometric dates from volcanic and plutonic rocks underlying it, igneous gravel it contains, from volcanic rocks, which interfinger with it, and fossils found in the overlying Cambridge Argillite, the Roxbury Conglomerate accumulated between 570 and 595 million years ago.
Igneous rock (igneous from Latin igneus 'fiery'), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust.
Dedham Granite is a pink to gray medium to coarse grained igneous rock. [3] It is phaneritic, meaning that the crystals are coarse enough to be seen with the naked eye. It is a two mica granite which means there are amounts of both muscovite mica and sericite present. There are also large amounts of quartz and Feldspar (mainly K-feldspar). [3]
This area has experienced extensive deformation which is expressed as pre-metamorphic faults, various folds, thrust faults, and doming. Evidence for igneous activity include the early-Devonian (408 Ma) diorites, early to mid-Devonian (390–400 Ma) granites, and the Carboniferous (360–350 Ma) granites. [5]
The change of rock composition most responsible for the creation of magma is the addition of water. Water lowers the solidus temperature of rocks at a given pressure. For example, at a depth of about 100 kilometers, peridotite begins to melt near 800 °C in the presence of excess water, but near 1,500 °C in the absence of water. [69]
1. A basic igneous rock of medium grain size, occurring as minor intrusions or in the central parts of thick lava flows. 2. A dark-coloured, basic, igneous rock, composed essentially of pyroxene and a triclinic feldspar with magnetic iron. Considered by some authors to be equivalent to a coarse-grained basalt. 3.