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Gabbro specimen Photomicrograph of a thin section of gabbro. Gabbro (/ ˈ ɡ æ b r oʊ / GAB-roh) is a phaneritic (coarse-grained and magnesium- and iron-rich), mafic intrusive igneous rock formed from the slow cooling magma into a holocrystalline mass deep beneath the Earth's surface.
Baltimore Gabbro Complex is a hypersthene gabbro with subordinate amounts of olivine gabbro, norite, anorthositic gabbro, and pyroxenite. Igneous minerals and textures are well preserved in some rocks, and other rocks exhibit varying degrees of alteration and recrystallization with a new metamorphic mineral assemblage.
The following is a list of rock types recognized by geologists.There is no agreed number of specific types of rock. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type.
Diabase (/ ˈ d aɪ. ə ˌ b eɪ s /), also called dolerite (/ ˈ d ɒ l. ə ˌ r aɪ t /) or microgabbro, [1] is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained to aphanitic chilled margins which may ...
These rock types can include: Mangerite: a pyroxene-bearing monzonite intrusive igneous rock; Charnockite: an orthopyroxene-bearing quartz-feldspar rock, once thought to be intrusive igneous, now recognized as metamorphic; Iron-rich felsic rocks, including monzonite and rapakivi granite; Iron-rich diorite, gabbro, and norite
To the east, the complex abuts and intrudes into the Rove Formation, an older structure of sedimentary rocks. Gabbro and diabase structures of the Duluth Complex trend generally from southwest to northeast, and differential erosion has left a series of ridges comprising these harder mafic rocks rising from the softer sedimentary rocks of the ...
Examples of phaneritic igneous rocks are gabbro, diorite, and granite. Porphyritic textures develop when conditions during the cooling of magma change relatively quickly. The earlier formed minerals will have formed slowly and remain as large crystals, whereas, sudden cooling causes the rapid crystallization of the remainder of the melt into a ...
The Sandy Group Gabbro is a member of the Roosevelt Gabbros that forms blobby irregular sills which are like small plutons. These intrusive blobs are internally differentiated, with the composition becoming increasingly more felsic upwards approaching the overlying Mount Scott Granite.