![\"North](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/North-Cascades_geomaps_sm.jpg\")
Metamorphism means, \u201cchange in form\u201d and metamorphic rocks result after existing rock forms are transformed.\u00a0 The original rock is subjected to heat and pressure, which causes profound physical and\/or chemical change.\u00a0 Metamorphism is the alteration of a parent rock into a metamorphic rock<\/i>.\u00a0 Metamorphism happens when the protolith<\/i> is subjected to heat and pressure because it is deep beneath the Earth\u2019s surface.<\/p>\n
(above) The North Cascades reveal many forms of metamorphic rocks.\u00a0 From skyline left to near right is Eldorado Peak composed of orthogneiss, Cascade Peak composed of schist, and Mixup Mt. composed of gneiss.<\/em><\/p>\n (above right) Detrital\/Clastic Quartz Sandstone, parent rock of quartzite, originates on the continental shelf or near shore on beaches, islands, lakes, stream channels or dunes.<\/em><\/p>\n (above) Metamorphism changed the mineral, chlorite, in<\/em>to this crystal druse of transparent quartz crystals found in Hot Springs, AR<\/em>.<\/p>\n Three Methods of Formation:<\/b>\u00a0 Three major classes of metamorphic rock are based upon the formation mechanism: Contact<\/i>, Barrovian<\/i>, and Regional<\/i>.<\/p>\n (left) Once shale, until altered by heat, this hornfels has a granular texture.\u00a0 Hornfels have granular, platy or elongate crystals that are randomly oriented so no foliation is evident.<\/em><\/p>\n (right) Once chlorite, until altered by pressure in<\/em>to feldspar, this <\/em>Labradorite, part of the feldspars group of minerals, can produce a colorful play of light across cleavage planes.\u00a0<\/em><\/p>\n (left) The granoblastic texture in this basic granulite reveals\u00a0 slight grain flattening fabric and was created by tectonic horizontal pressure, friction and distortion.<\/em><\/p>\n Two Classifications of Texture:\u00a0 <\/b>Metamorphic rocks can be classified by grain size and the degree of foliation<\/i>. The two distinctive metamorphic textures are Foliation<\/i> and Granular<\/i> (non-foliated).\u00a0 Foliated means the minerals are layers.\u00a0 Non-foliated means the grains are equidimensional<\/i>.\u00a0 Well-developed foliation is characteristic of most metamorphic rocks. Metamorphic rocks often break easily along foliation planes (the planes of layers).<\/p>\n (above left) This soapstone has a granulated, non-foliated crystalline texture and is composed of one mineral.\u00a0 It is a talc rich metamorphic rocks.\u00a0 Pure talcose soapstone is called steatite.<\/em><\/p>\n (above right) Altered from slate, this phyllite shows bands of color from various minerals.\u00a0 It has fine-grained mica flakes in a preferred orientation whereas slate has extremely fine clay flakes that achieve a preferred orientation.\u00a0<\/em><\/p>\n (right) Altered from shale, this slate reveals a type of foliation known as “slaty cleavage”. Note the grains of mica, quartz, and ilmenite aligned with a preferred orientation.<\/em> <\/p>\n (right) Altered from mudstone\/shale into a higher degree of crystallization than slate, this schist example reveals the characteristic “scaly” schistose texture, caused by platy micas.\u00a0<\/em><\/p>\n (right) Altered from sedimentary of felsic igneous rocks, and subjected to higher temperatures and pressures than schist, this gneiss example is foliated and displays mineral banding.\u00a0 The foliations are characterized by alternating darker and lighter colored sub-parallel bands, called \u201cgneissic banding”.<\/em><\/p>\n Eight Common Metamorphic Rocks:<\/b><\/p>\n (right) Mylonite, one of 8 common metamorphic rocks, has been put through the mill.\u00a0 It is formed during intense shearing encountered during folding and faulting, which nearly pulverizes the parent rock.\u00a0 It is fine grained, foliated and very hard.<\/em><\/p>\n Six Common Metamorphic Building Materials<\/b>.\u00a0 For the purposes of masonry, the most commonly used building materials for building facings and paving are marble, quartzite, and gneiss.\u00a0 Schist can be used for paving.\u00a0 Slate and phyllite can be used for flooring and floor tiles.<\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" Metamorphism means, \u201cchange in form\u201d and metamorphic rocks result after existing rock forms are transformed.\u00a0 The original rock is subjected to heat and pressure, which causes profound physical and\/or chemical change.\u00a0 Metamorphism is the alteration of a parent rock into a metamorphic rock.\u00a0 Metamorphism happens when the protolith is subjected to heat and pressure because … <\/p>\n![\"Quartz](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/Quartz-Sandstone_core_sm.gif\")
Parent Rock.\u00a0 <\/b>The protolithic<\/i> or original rock may be sedimentary rock or igneous rock or an older metamorphic rock.\u00a0 However, most metamorphic rocks come from three sedimentary parent rocks: Sandstone<\/i>, Limestone<\/i>, and Shale<\/i>.<\/p>\n\n
![\"Quartz](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/Quartz-Mineral_webmineral_sm.jpg\")
Changes.\u00a0 <\/b>Pressure and temperature cause mineral, texture and rock changes.<\/p>\n\n
![\"hornfels](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/hornfels-granular_auckland.jpg\")
Heat<\/b>.\u00a0 Contact Metamorphism<\/i> happens when the protolith is subjected to heat from the intrusion of magma<\/i> or hot molten rock from the Earth\u2019s interior.\u00a0 The metamorphic result has a granular or hornfeisic<\/i> texture.\u00a0 For example heat will change the mineral clay texture of shale into Hornfels <\/i>with a granular texture.<\/p>\n![\"feldspar](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/feldspar-labradorite_galleries.jpg\")
Pressure<\/b>.\u00a0 Barrovian (Burial) Metamorphism<\/i> happens when the protolith is subjected to pressure.\u00a0 The metamorphic result has a banded texture.\u00a0 For example pressure will change the mineral, chlorite,<\/i> into the minerals of quartz, feldspar<\/i> and mica<\/i>.<\/p>\n![\"gloss_granoblastic_imperial\"](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/gloss_granoblastic_imperial-267x300.jpg\")
Mountain-building<\/b>.\u00a0 Regional<\/i> or Dynamic Metamorphism<\/i> happens when the protolith is subjected to temperature and pressure from tectonic<\/i> processes.\u00a0 \u00a0Typically in mountain-building regions the protolith is subjected to horizontal pressure, friction and distortion.\u00a0 The metamorphic result can have a slaty<\/i> texture (Slate, Phyllite), a schistose<\/i> texture (Schist), a gneissose<\/i> texture (Gneiss), or a granoblastic<\/i> texture (Granulite).<\/p>\n![\"soapstone_Newark\"](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/soapstone_Newark.jpg\")
Granular Texture.\u00a0 <\/b>Granular rocks are usually composed of one mineral.\u00a0 For example quartz forms Quartzite and calcite forms Marble.\u00a0 Granular<\/i> describes a metamorphic rock consisting of interlocking crystals or granules, that are almost entirely composed of one mineral. A granular texture is developed if a rock’s chemical composition is close to that of a particular mineral. This mineral will crystallize if the rock is subjected to high pressure and temperature. A granular texture is characteristic of some metamorphic rocks.\u00a0 Non-foliated textures include Marble, Soapstone<\/i>, and Serpentine<\/i>, as well as Quartzite<\/i> and Hornfels<\/i>.<\/p>\n![\"Phyllite](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/Phyllite-foliation_USGOV.jpg\")
Foliation Texture.\u00a0 <\/b>Foliation<\/i> represents a distinct plane of weakness in the rock. Foliation is caused by the re-alignment of minerals when they are subjected to high pressure and temperature. \u00a0Foliation occurs during the recrystallization process when planar patterns of strain form layers that reveal bands showing the colors of the minerals that formed within.\u00a0 Varieties of foliated textures are Schist, Gneiss, Slate, Phyllite<\/i> and Mylonite<\/i>.<\/p>\n![\"Slaty_cleavage_Wiki\"](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/Slaty_cleavage_Wiki.jpg\")
Three Foliation Layers:<\/b>\u00a0 With foliation, new metamorphic minerals line up to produce distinct layering in the rock with three different looks: slaty cleavage <\/i>(Slate), schistosity <\/i>(Schist), and mineral banding <\/i>(Gneiss).\u00a0 <\/i><\/p>\n
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![\"Schist](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/08\/Schist-banding_auckland.jpg\")
Slaty Cleavage has clay minerals converted to chlorite<\/i> that line up.<\/li>\n![\"Gneiss](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/Gneiss-mineral-banding_auckland.jpg\")
<\/b><\/p>\n\n
![\"mylonite](\"https:\/\/waltonsons.com\/wp\/wp-content\/uploads\/2014\/09\/mylonite-rock_auckland.jpg\")
Hornfels <\/b>is fine-grained and derives from clay-rich rock altered by high heat.<\/li>\n<\/ul>\n