- gneiss - slate. It is a metamorphic rock that is coarse and foliated with alternate bands of granular minerals and flaky or dark minerals. Geology (from Ancient Greek (g) 'earth', and o () 'study of, discourse') is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. In traditional English and North American usage, a gneiss is a coarse-grained metamorphic rock showing compositional banding (gneissic banding) but poorly developed schistosity and indistinct cleavage.In other words, it is a metamorphic rock composed of mineral grains easily seen with the unaided eye, which form obvious compositional layers, but which has only a weak tendency It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole.Hornblende minerals are common in igneous and metamorphic rocks.. Identify the minerals in it as feldspar, quartz, and either mica or hornblende, the same as in granite, specimen No. Gneiss is usually light in color, but it can be quite dark. Amphibolite - A gneiss or schist largely made up of amphibole and plagioclase minerals. Modern geology significantly overlaps all other Earth sciences, including hydrology, and so is treated as one Gneiss is usually light in color, but it can be quite dark. Crystal structure of pyrope garnet. The first set of criteria describes how easily the cleavage is obtained. Beryl (/ b r l / BERR-l) is a mineral composed of beryllium aluminium silicate with the chemical formula Be 3 Al 2 Si 6 O 18. Typically, these rocks split along parallel, planar surfaces. It is a metamorphic rock that is coarse and foliated with alternate bands of granular minerals and flaky or dark minerals. Cleavage is a term used to describe minerals that break in a predictable way. Cleavage is considered perfect if it is easily obtained and the cleavage planes are easily distinguished. Biotite is a common rock-forming mineral, and is especially noted in metamorphic rocks such as schist and gneiss. Second, the more distinct the color change, the higher the value.Alexandrites can exhibit everything from 100% to just 5% color change. Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock.It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks generally indicates metamorphism deep in the Earth's crust.Kyanite is also known as disthene or cyanite.. Kyanite is strongly anisotropic, in These minerals are found throughout the world in metamorphic, igneous, and Important Terms in Measurement The first set of criteria describes how easily the cleavage is obtained. Certain rocks or minerals to break along specific planes where weak bonds are present. Study the specimen carefully as a whole, and note that it comes under E in the Table. Study the specimen carefully as a whole, and note that it comes under E in the Table. Garnet is the name used for a large group of rock-forming minerals.These minerals share a common crystal structure and a generalized chemical composition of X 3 Y 2 (SiO 4) 3.In that composition, "X" can be Ca, Mg, Fe 2+ or Mn 2+, and "Y" can be Al, Fe 3+, Mn 3+, V 3+ or Cr 3+.. Identify the minerals in it as feldspar, quartz, and either mica or hornblende, the same as in granite, specimen No. Slaty cleavage is composed of platy minerals that are too small to see. First, the closer the colors to pure green and red, the higher the value. Rocks and Minerals is an identification event for the 2022 and 2023 seasons in both Division B and Division C in which teams use their knowledge of rocks and minerals to identify pictures/specimens and complete a written test.. It looks like it has ribbons or stripes of minerals running through the rock. Andalusite is an aluminosilicate mineral with a chemical composition of Al 2 SiO 5.It forms at low to medium metamorphic temperatures and pressures where argillaceous rocks (such as shale) are exposed to regional and contact metamorphism.. Andalusite is a rock-forming mineral most commonly found in schist, gneiss, and hornfels.Minor amounts are also In traditional English and North American usage, a gneiss is a coarse-grained metamorphic rock showing compositional banding (gneissic banding) but poorly developed schistosity and indistinct cleavage.In other words, it is a metamorphic rock composed of mineral grains easily seen with the unaided eye, which form obvious compositional layers, but which has only a weak tendency The official Rocks and Minerals List for 2018 includes specific rocks and minerals covered in the event. 18k yellow gold, 1-ct ruby, and 0.15 ctw diamonds. Cleavage - The tendency of a mineral to split along crystallographic planes. The geology of Tasmania is complex, with the world's biggest exposure of diabase, or dolerite.The rock record contains representatives of each period of the Neoproterozoic, Paleozoic, Mesozoic and Cenozoic eras. Study the specimen carefully as a whole, and note that it comes under E in the Table. Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock.It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks generally indicates metamorphism deep in the Earth's crust.Kyanite is also known as disthene or cyanite.. Kyanite is strongly anisotropic, in coarse-grained texture. Spodumene is the most common source of high-grade lithium. Glassy luster; hardness of 6.5 to 7. Are structures that develop in sedimentary or igneous rocks after lithification, and in metamorphic rocks during or after their formation. The official Rocks and Minerals List for 2018 includes specific rocks and minerals covered in the event. It's typically translucent and commonly takes on a delicate lavender or violet shade. Note from the rounded pebbles and grains of quartz, etc., that the specimen comes under F in the Table. Fundamental secondary structures are joints and shear fractures; faults, folds, cleavage, foliations, lineations, shear zones (Davis & Reynolds, 1996). It is considered good if the cleavage is produced with some difficulty but has obvious cleavage planes. Crystal structure of pyrope garnet. Brazil has been the world's leading source of tourmaline for nearly 500 years. Hornblende is a complex inosilicate series of minerals. These minerals are found throughout the world in metamorphic, igneous, and When minerals break along planes in which chemical bonds are weak, they produce flat surfaces called cleavage planes. Cleavage is considered perfect if it is easily obtained and the cleavage planes are easily distinguished. 18k yellow gold, 1-ct ruby, and 0.15 ctw diamonds. The west coast region hosts This is a beautiful antique ring, but the ruby and diamonds have received native cuts. Biotite is also the primary mica in rare earth pegmatites. Spodumene is the most common source of high-grade lithium. It is harder than a streak plate, and has a specificgravity of 2.65. Magnesite, MgCO3 is found in serpentine rock as a hard, non-crystalline mineral, with a fracture like broken porcelain; it is also found in talc schist and other magnesian rocks. Garnets do not have any cleavage planes, so when they fracture under stress, sharp, irregular pieces are formed. Andalusite is an aluminosilicate mineral with a chemical composition of Al 2 SiO 5.It forms at low to medium metamorphic temperatures and pressures where argillaceous rocks (such as shale) are exposed to regional and contact metamorphism.. Andalusite is a rock-forming mineral most commonly found in schist, gneiss, and hornfels.Minor amounts are also Its pyroxene cleavage is combined with a splintery fracture. The first set of criteria describes how easily the cleavage is obtained. Corundum does display parting perpendicular to the c-axis. coarse-grained texture. Slaty cleavage is not always in the same direction as the original sedimentary bedding planes, thus any fossils originally in the rock are usually erased, but sometimes they survive in smeared or stretched form. 1; this specimen is gneiss. Second, the more distinct the color change, the higher the value.Alexandrites can exhibit everything from 100% to just 5% color change. The mineral has a Mohs hardness of 5 + 1 2 to 6, between apatite and feldspar. The geology of Tasmania is complex, with the world's biggest exposure of diabase, or dolerite.The rock record contains representatives of each period of the Neoproterozoic, Paleozoic, Mesozoic and Cenozoic eras. Corundum does display parting perpendicular to the c-axis. Corundum does display parting perpendicular to the c-axis. Important Terms in Measurement Clear spodumene can also be a lilac color, in which case it is known as the gemstone kunzite. When minerals break along planes in which chemical bonds are weak, they produce flat surfaces called cleavage planes. The 2018 identification list can be Brookite is a brittle mineral, with a subconchoidal to irregular fracture and poor cleavage in one direction parallel to the c crystal axis and traces of cleavage in a direction perpendicular to both the a and the b crystal axes. Tourmaline Sources. It is also found in igneous rock such as granites and rhyolites. Biotite is a common rock-forming mineral, and is especially noted in metamorphic rocks such as schist and gneiss. is stable at high pressures and temperatures and is thus found in green-schist facies metamorphic rocks including gneiss, hornblende schist, and mica schist. Typically, these rocks split along parallel, planar surfaces. Granite and gabbro have a similar _____. It breaks with a conchoidal fracture but displays no cleavage. Cleavage is a term used to describe minerals that break in a predictable way. What is Andalusite? Quartz is a hard, crystalline mineral composed of silica (silicon dioxide).The atoms are linked in a continuous framework of SiO 4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO 2.Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.. Quartz exists in two forms, the normal Fracture - A break in the rock, the opening of which allows mineral-bearing solutions to enter. What is Garnet? Tourmaline Sources. The 2018 identification list can be Note from the rounded pebbles and grains of quartz, etc., that the specimen comes under F in the Table. Important Terms in Measurement In the 1500s Portuguese explorers obtained green and blue tourmaline from indigenous people and from panning streams in search of gold.They thought that these colorful stones were emeralds and sapphires and sent them back to Portugal, where they were cut into gems and In the 1500s Portuguese explorers obtained green and blue tourmaline from indigenous people and from panning streams in search of gold.They thought that these colorful stones were emeralds and sapphires and sent them back to Portugal, where they were cut into gems and It is harder than a streak plate, and has a specificgravity of 2.65. Its pyroxene cleavage is combined with a splintery fracture. Granite and gabbro have a similar _____. With further metamorphism, slate turns to phyllite, then to schist or gneiss. With further metamorphism, slate turns to phyllite, then to schist or gneiss. Well-known varieties of beryl include emerald and aquamarine.Naturally occurring, hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Geology (from Ancient Greek (g) 'earth', and o () 'study of, discourse') is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. The grain size is usually fairly coarse. Amphibolite - A gneiss or schist largely made up of amphibole and plagioclase minerals. Andalusite is an aluminosilicate mineral with a chemical composition of Al 2 SiO 5.It forms at low to medium metamorphic temperatures and pressures where argillaceous rocks (such as shale) are exposed to regional and contact metamorphism.. Andalusite is a rock-forming mineral most commonly found in schist, gneiss, and hornfels.Minor amounts are also Brookite is a brittle mineral, with a subconchoidal to irregular fracture and poor cleavage in one direction parallel to the c crystal axis and traces of cleavage in a direction perpendicular to both the a and the b crystal axes. Gneiss usually breaks into blocky pieces, not along the layers. Garnets do not have any cleavage planes, so when they fracture under stress, sharp, irregular pieces are formed. What is Garnet? Its pyroxene cleavage is combined with a splintery fracture. Beryl (/ b r l / BERR-l) is a mineral composed of beryllium aluminium silicate with the chemical formula Be 3 Al 2 Si 6 O 18. For many good examples of mineral fracture and cleavage, watch the video linked below: blank Video 3-6: Examples of mineral fracture and cleavage (8 minutes) A good additional perspective on cleavage can be found at: blank Video 3-7: Mineral cleavage (5 minutes) 3.5.3 Hardness. Alexandrites have two primary value drivers. It does not reactwith hydrochloric acid, is a light pink color, and has a nonmetallic luster. Gneiss. - gneiss - slate. The grain size is usually fairly coarse. Hardness is a minerals resistance to abrasion or scratching. For many good examples of mineral fracture and cleavage, watch the video linked below: blank Video 3-6: Examples of mineral fracture and cleavage (8 minutes) A good additional perspective on cleavage can be found at: blank Video 3-7: Mineral cleavage (5 minutes) 3.5.3 Hardness. Slate is usually dark, but it can be colorful too. Cleavage - The tendency of a mineral to split along crystallographic planes. The general formula is (Ca,Na) 2-3 (Mg,Fe,Al) 5 (Al,Si) 8 O 22 (OH,F) 2 While these cuts retain much of the mass of the rough stones, the resulting gems have irregular shapes and dont look very lively. Note from the rounded pebbles and grains of quartz, etc., that the specimen comes under F in the Table. The crystalline variety is found in crystalline limestone and dolomite that have been changed by intrusions of gabbro and other basic and intermediate rocks. First, the closer the colors to pure green and red, the higher the value. What is Andalusite? Biotite is also the primary mica in rare earth pegmatites. It is considered good if the cleavage is produced with some difficulty but has obvious cleavage planes. is stable at high pressures and temperatures and is thus found in green-schist facies metamorphic rocks including gneiss, hornblende schist, and mica schist. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole.Hornblende minerals are common in igneous and metamorphic rocks.. Brazil has been the world's leading source of tourmaline for nearly 500 years. Cleavage. Magnesite, MgCO3 is found in serpentine rock as a hard, non-crystalline mineral, with a fracture like broken porcelain; it is also found in talc schist and other magnesian rocks. Slaty cleavage is composed of platy minerals that are too small to see. Twinning is uncertain. Spodumene is the most common source of high-grade lithium. Phyllitic foliation is composed of platy minerals that are slightly larger than those found in slaty cleavage, but generally are still too small to see with the unaided eye. While these cuts retain much of the mass of the rough stones, the resulting gems have irregular shapes and dont look very lively. Phyllitic foliation is composed of platy minerals that are slightly larger than those found in slaty cleavage, but generally are still too small to see with the unaided eye. Identify the minerals in it as feldspar, quartz, and either mica or hornblende, the same as in granite, specimen No. It is harder than a streak plate, and has a specificgravity of 2.65. Rocks and Minerals is an identification event for the 2022 and 2023 seasons in both Division B and Division C in which teams use their knowledge of rocks and minerals to identify pictures/specimens and complete a written test.. Well-known varieties of beryl include emerald and aquamarine.Naturally occurring, hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Geology (from Ancient Greek (g) 'earth', and o () 'study of, discourse') is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. It is one of the few southern hemisphere areas that were glaciated during the Pleistocene with glacial landforms in the higher parts. While these cuts retain much of the mass of the rough stones, the resulting gems have irregular shapes and dont look very lively. Second, the more distinct the color change, the higher the value.Alexandrites can exhibit everything from 100% to just 5% color change. Cleavage is a term used to describe minerals that break in a predictable way. Magnesite, MgCO3 is found in serpentine rock as a hard, non-crystalline mineral, with a fracture like broken porcelain; it is also found in talc schist and other magnesian rocks. It breaks with a conchoidal fracture but displays no cleavage. coarse-grained texture. Cleavage: None. Quartz is a hard, crystalline mineral composed of silica (silicon dioxide).The atoms are linked in a continuous framework of SiO 4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO 2.Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.. Quartz exists in two forms, the normal Modern geology significantly overlaps all other Earth sciences, including hydrology, and so is treated as one Twinning is uncertain. 1; this specimen is gneiss. The official Rocks and Minerals List for 2018 includes specific rocks and minerals covered in the event. Fracture - A break in the rock, the opening of which allows mineral-bearing solutions to enter. Slaty cleavage is not always in the same direction as the original sedimentary bedding planes, thus any fossils originally in the rock are usually erased, but sometimes they survive in smeared or stretched form. Typically, these rocks split along parallel, planar surfaces. Cleavage: None. These minerals are found throughout the world in metamorphic, igneous, and It is one of the few southern hemisphere areas that were glaciated during the Pleistocene with glacial landforms in the higher parts. Fundamental secondary structures are joints and shear fractures; faults, folds, cleavage, foliations, lineations, shear zones (Davis & Reynolds, 1996). Cleavage/Fracture. 18k yellow gold, 1-ct ruby, and 0.15 ctw diamonds. The west coast region hosts Slaty cleavage is composed of platy minerals that are too small to see. Cleavage/Fracture. Granular minerals usually consist of feldspar or quartz, while flaky minerals are pyroxenes. The mineral has a Mohs hardness of 5 + 1 2 to 6, between apatite and feldspar. Modern geology significantly overlaps all other Earth sciences, including hydrology, and so is treated as one Rock Type: Igneous, Metamorphic: Popularity (1-4) 2: Prevalence (1-3) 1: Demand (1-3) 2 Hardness is a minerals resistance to abrasion or scratching. What is Andalusite? Granite and gabbro have a similar _____. What is Garnet? Clear spodumene can also be a lilac color, in which case it is known as the gemstone kunzite. Cleavage is defined using two sets of criteria. Are structures that develop in sedimentary or igneous rocks after lithification, and in metamorphic rocks during or after their formation. It is a metamorphic rock that is coarse and foliated with alternate bands of granular minerals and flaky or dark minerals. Slate is usually dark, but it can be colorful too. Cleavage is considered perfect if it is easily obtained and the cleavage planes are easily distinguished. Alexandrites have two primary value drivers. Cleavage/Fracture. Slaty cleavage is not always in the same direction as the original sedimentary bedding planes, thus any fossils originally in the rock are usually erased, but sometimes they survive in smeared or stretched form. Slate is usually dark, but it can be colorful too. For many good examples of mineral fracture and cleavage, watch the video linked below: blank Video 3-6: Examples of mineral fracture and cleavage (8 minutes) A good additional perspective on cleavage can be found at: blank Video 3-7: Mineral cleavage (5 minutes) 3.5.3 Hardness. is stable at high pressures and temperatures and is thus found in green-schist facies metamorphic rocks including gneiss, hornblende schist, and mica schist. Cleavage is defined using two sets of criteria. Pure beryl is colorless, but it is frequently tinted by Glassy luster; hardness of 6.5 to 7. 1; this specimen is gneiss. Pure beryl is colorless, but it is frequently tinted by In the 1500s Portuguese explorers obtained green and blue tourmaline from indigenous people and from panning streams in search of gold.They thought that these colorful stones were emeralds and sapphires and sent them back to Portugal, where they were cut into gems and Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock.It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks generally indicates metamorphism deep in the Earth's crust.Kyanite is also known as disthene or cyanite.. Kyanite is strongly anisotropic, in The west coast region hosts Granular minerals usually consist of feldspar or quartz, while flaky minerals are pyroxenes. Hornblende is a complex inosilicate series of minerals. It looks like it has ribbons or stripes of minerals running through the rock. Certain rocks or minerals to break along specific planes where weak bonds are present. The geology of Tasmania is complex, with the world's biggest exposure of diabase, or dolerite.The rock record contains representatives of each period of the Neoproterozoic, Paleozoic, Mesozoic and Cenozoic eras. The general formula is (Ca,Na) 2-3 (Mg,Fe,Al) 5 (Al,Si) 8 O 22 (OH,F) 2 Quartz is a hard, crystalline mineral composed of silica (silicon dioxide).The atoms are linked in a continuous framework of SiO 4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO 2.Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.. Quartz exists in two forms, the normal Cleavage - The tendency of a mineral to split along crystallographic planes. The crystalline variety is found in crystalline limestone and dolomite that have been changed by intrusions of gabbro and other basic and intermediate rocks. Fundamental secondary structures are joints and shear fractures; faults, folds, cleavage, foliations, lineations, shear zones (Davis & Reynolds, 1996). Cleavage. Glassy luster; hardness of 6.5 to 7. Gneiss. Biotite is also the primary mica in rare earth pegmatites. Gneiss usually breaks into blocky pieces, not along the layers. Rock Type: Igneous, Metamorphic: Popularity (1-4) 2: Prevalence (1-3) 1: Demand (1-3) 2 Gneiss usually breaks into blocky pieces, not along the layers. It is one of the few southern hemisphere areas that were glaciated during the Pleistocene with glacial landforms in the higher parts. Granular minerals usually consist of feldspar or quartz, while flaky minerals are pyroxenes. This is a beautiful antique ring, but the ruby and diamonds have received native cuts. First, the closer the colors to pure green and red, the higher the value. It is also found in igneous rock such as granites and rhyolites. Phyllitic foliation is composed of platy minerals that are slightly larger than those found in slaty cleavage, but generally are still too small to see with the unaided eye. - gneiss - slate. Hornblende is a complex inosilicate series of minerals. Cleavage. Garnet is the name used for a large group of rock-forming minerals.These minerals share a common crystal structure and a generalized chemical composition of X 3 Y 2 (SiO 4) 3.In that composition, "X" can be Ca, Mg, Fe 2+ or Mn 2+, and "Y" can be Al, Fe 3+, Mn 3+, V 3+ or Cr 3+.. Amphibolite - A gneiss or schist largely made up of amphibole and plagioclase minerals. The general formula is (Ca,Na) 2-3 (Mg,Fe,Al) 5 (Al,Si) 8 O 22 (OH,F) 2 The 2018 identification list can be Twinning is uncertain. Biotite is a common rock-forming mineral, and is especially noted in metamorphic rocks such as schist and gneiss. It looks like it has ribbons or stripes of minerals running through the rock. It does not reactwith hydrochloric acid, is a light pink color, and has a nonmetallic luster. It is considered good if the cleavage is produced with some difficulty but has obvious cleavage planes. Well-known varieties of beryl include emerald and aquamarine.Naturally occurring, hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Brookite is a brittle mineral, with a subconchoidal to irregular fracture and poor cleavage in one direction parallel to the c crystal axis and traces of cleavage in a direction perpendicular to both the a and the b crystal axes. Pure beryl is colorless, but it is frequently tinted by Cleavage is defined using two sets of criteria. Rock Type: Igneous, Metamorphic: Popularity (1-4) 2: Prevalence (1-3) 1: Demand (1-3) 2 With further metamorphism, slate turns to phyllite, then to schist or gneiss. Beryl (/ b r l / BERR-l) is a mineral composed of beryllium aluminium silicate with the chemical formula Be 3 Al 2 Si 6 O 18. It's typically translucent and commonly takes on a delicate lavender or violet shade. Are structures that develop in sedimentary or igneous rocks after lithification, and in metamorphic rocks during or after their formation. Gneiss. Tourmaline Sources. Brazil has been the world's leading source of tourmaline for nearly 500 years. The mineral has a Mohs hardness of 5 + 1 2 to 6, between apatite and feldspar. It's typically translucent and commonly takes on a delicate lavender or violet shade. Hardness is a minerals resistance to abrasion or scratching. Cleavage: None. The grain size is usually fairly coarse. The crystalline variety is found in crystalline limestone and dolomite that have been changed by intrusions of gabbro and other basic and intermediate rocks. Alexandrites have two primary value drivers. It is also found in igneous rock such as granites and rhyolites. Rocks and Minerals is an identification event for the 2022 and 2023 seasons in both Division B and Division C in which teams use their knowledge of rocks and minerals to identify pictures/specimens and complete a written test.. Clear spodumene can also be a lilac color, in which case it is known as the gemstone kunzite. It breaks with a conchoidal fracture but displays no cleavage. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole.Hornblende minerals are common in igneous and metamorphic rocks.. Gneiss is usually light in color, but it can be quite dark. Fracture - A break in the rock, the opening of which allows mineral-bearing solutions to enter. When minerals break along planes in which chemical bonds are weak, they produce flat surfaces called cleavage planes. In traditional English and North American usage, a gneiss is a coarse-grained metamorphic rock showing compositional banding (gneissic banding) but poorly developed schistosity and indistinct cleavage.In other words, it is a metamorphic rock composed of mineral grains easily seen with the unaided eye, which form obvious compositional layers, but which has only a weak tendency Crystal structure of pyrope garnet. It does not reactwith hydrochloric acid, is a light pink color, and has a nonmetallic luster. Certain rocks or minerals to break along specific planes where weak bonds are present. This is a beautiful antique ring, but the ruby and diamonds have received native cuts. Garnets do not have any cleavage planes, so when they fracture under stress, sharp, irregular pieces are formed. Garnet is the name used for a large group of rock-forming minerals.These minerals share a common crystal structure and a generalized chemical composition of X 3 Y 2 (SiO 4) 3.In that composition, "X" can be Ca, Mg, Fe 2+ or Mn 2+, and "Y" can be Al, Fe 3+, Mn 3+, V 3+ or Cr 3+..