A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than 1 cm (0.4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic composition to granite. However, rarer intermediate composition and mafic pegmatites are known.
Schist is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes or plates. This texture reflects a high content of platy minerals, such as micas, talc, chlorite, or graphite. These are often interleaved with more granular minerals, such as feldspar or quartz.
Quartz monzonite is an intrusive, felsic, igneous rock that has an approximately equal proportion of orthoclase and plagioclase feldspars. It is typically a light colored phaneritic (coarse-grained) to porphyritic granitic rock. The plagioclase is typically intermediate to sodic in composition, andesine to oligoclase. Quartz is present in significant amounts. Biotite and/or hornblende constitute the dark minerals. Because of its coloring, it is often confused with granite, but whereas granite contains more than 20% quartz, quartz monzonite is only 5–20% quartz. Rock with less than five percent quartz is classified as monzonite. A rock with more alkali feldspar is a syenite whereas one with more plagioclase is a quartz diorite. The fine grained volcanic rock equivalent of quartz monzonite is quartz latite.
Granodiorite is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar.
The Spruce Pine Mining District is a swath of the valley of the North Toe River in the Blue Ridge Mountains of northwestern North Carolina. The area is mined for its mica, kaolin, quartz and feldspar. Spruce Pine district is one of the largest suppliers of high-purity quartz, which is used in the manufacture of silicon for integrated circuits. The district is named after the town of Spruce Pine, which is located in the middle of the region and is the hub of major mining activity there. The district is approximately 25 miles long and 5 miles wide.
Litchfieldite is a rare igneous rock. It is a coarse-grained, foliated variety of nepheline syenite, sometimes called nepheline syenite gneiss or gneissic nepeheline syenite. Litchfieldite is composed of two varieties of feldspar, with nepheline, sodalite, cancrinite and calcite. The mafic minerals, when present, are magnetite and an iron-rich variety of biotite (lepidomelane).
Syenogranite is a fine to coarse grained intrusive igneous rock of the same general composition as granite. They are characteristically felsic.
Barre granite /ˈbæri/ is a Devonian granite pluton near the town of Barre in Washington County, Vermont. Richardson described it as a "fine granite, composed of quartz, feldspar, and mica. The mica is both muscovite and biotite." It intrudes into the Waits River Formation.
The Woodstock Quartz Monzonite is a Silurian or Ordovician quartz monzonite pluton in Baltimore County, Maryland. It is described as a massive biotite-quartz monzonite which intrudes through the Baltimore Gneiss at a single locality surrounding the town of Granite, Maryland.
The Norbeck Intrusive Suite is an Ordovician granitic pluton in Montgomery County, Maryland. The intrusive suite was originally mapped as the Norbeck Quartz Diorite by Hopson, and is shown as such on the Geologic Map of Maryland of 1968. A. A. Drake later revised the name after more detailed mapping. It intrudes through the Wissahickon Formation.
The Ellicott City Granodiorite is a Silurian or Ordovician granitic pluton in Howard and Baltimore Counties, Maryland. It is described as a biotite granodiorite along the margin of the intrusion which grades into a quartz monzonite in its core. It intrudes through the Wissahickon Formation and the Baltimore Gabbro Complex.
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 Port Deposit Gneiss is a Paleozoic gneiss formation in Cecil County, Maryland. It is described as a "Moderately to strongly deformed intrusive complex, chiefly composed of quartz diorite gneiss. Rock types include gneissic biotite-quartz diorite, hornblende-biotite-quartz diorite, and biotite granodiorite, with minor amounts of quartz monzonite and hornblende-quartz diorite. Moderate protoclastic foliation grades into strong cataclastic shearing." It intrudes into the Volcanic Complex of Cecil County.
The Oella Formation is a Late Proterozoic or early Cambrian schist in Howard and Baltimore Counties, Maryland. It is described as "Medium-grained biotite-plagioclase-muscovite-quartz schist, locally garnetiferous, interlayered on a centimeter to decimeter scale with fine-grained biotite-plagioclase-quartz gneiss, commonly bearing muscovite but less commonly garnet."
The Baltimore Gneiss is a Precambrian geological formation in the Piedmont region of Maryland, Pennsylvania, and Delaware.
The San Miguel gneiss is a Paleoproterozoic pluton in the Nacimiento Mountains of New Mexico. It has a radiometric age of 1.695 billion years, corresponding to the Statherian period.
The Joaquin quartz monzonite is a Mesoproterozoic pluton in northern New Mexico. Radiometric dating gives it an age of 1460 million years, corresponding to the Calymmian period.
The Lilesville Granite, also referred to as the Lilesville pluton, is a ring-shaped body of granitic rock that spans about 94 square miles (240 km2) in Anson, Richmond, and Montgomery Counties in southern North Carolina.
The Guilford Quarry Pratt Through Truss Bridge at Guilford, Maryland is a single-span, metal truss, railroad bridge
The Boscobel complex is unit of interlayered granite and gneiss within Goochland and Powhatan Counties, Virginia. The area had been mapped as the Petersburg Granite in 1970 by B. K. Goodwin.
