A6 Common Rock Types
321
Sedimentary Rocks. Consolidated sediments. Particle assemblages consisting of minerals, rock
fragments, shell, and amorphous substances in various proportions. Produced by weathering, transportation, deposition, alteration, and cementation. Classification is by grain size and composition
(see Chap. 3).
Detrital or Clastic Rocks
(U nconsolidated)
(Consolidated)
Gravel
Conglomerate
Sand
Sandstone
&It
<More
Clay
Mud a )
Claystone
Mudstone
Shale b )
Decreasing
grain-size
a)Mud is a mixture of silt and clay.
b)Shale is the most common sedimentary rock, it is siltstone, claystone, and mudstone which is
laminated and parts along bedding planes.
Examples of common sand- and siltstones are:
Quartz sandstone: produced through recycling of sedimentary rocks (quartz is resistant to weathering)
Arkose: feldspar-rich sandstone, produced from erosion of granite and granodiorite
Graywacke: cemented "dirty" sand, that is, with abundant clay and rock fragments. Composition is
similar to that of sediments accumulating on active margins (see Fig. 2.7).
Chemical Rocks. Assemblages of minerals produced by precipitation from watery solution, either
by organisms or inorganically. Classification is by origin and composition.
(Biogenous)
(Nonbiogenous)
Reef-limestone
Dolomite
Bedded limestone
Evaporite
Chert a )
Coal
Phosphorite
a) Chert denotes a series of rocks ranging from silicified mudstones to very fine-grained quartz rock.
The origin of the silica (quartz) is biogenous opal (at least in Mesozoic and younger rocks).
Metamorphic Rocks. Mineral assemblages produced by defonnation and recrystallization of
igenous rocks or sedimentary rocks through elevated temperature and pressure, with or without
addition of material through injection of solutions. Classification is by degree of foliation, types of
minerals present, and grain size. Metamorphic rocks occur at active margins (see Fig. 2.7).
(Nonfoliated)
Hornfels (from shale, tuff, or lava)
Marble (from limestone or dolomite)
Quartzite (from quartz sandstone)
Amphibolite (from basaltic material or corresp. sediments)
Granulite (from shale, graywacke, or andesite)
(Foliated)
Slate (from shale, tuff)
Schist (from basalt, andesite, tuff, or shale)
Gneiss (from granite, diorite, schist, shale, etc)
Source for A6, any geology text book
321
Sedimentary Rocks. Consolidated sediments. Particle assemblages consisting of minerals, rock
fragments, shell, and amorphous substances in various proportions. Produced by weathering, transportation, deposition, alteration, and cementation. Classification is by grain size and composition
(see Chap. 3).
Detrital or Clastic Rocks
(U nconsolidated)
(Consolidated)
Gravel
Conglomerate
Sand
Sandstone
&It
<More
Clay
Mud a )
Claystone
Mudstone
Shale b )
Decreasing
grain-size
a)Mud is a mixture of silt and clay.
b)Shale is the most common sedimentary rock, it is siltstone, claystone, and mudstone which is
laminated and parts along bedding planes.
Examples of common sand- and siltstones are:
Quartz sandstone: produced through recycling of sedimentary rocks (quartz is resistant to weathering)
Arkose: feldspar-rich sandstone, produced from erosion of granite and granodiorite
Graywacke: cemented "dirty" sand, that is, with abundant clay and rock fragments. Composition is
similar to that of sediments accumulating on active margins (see Fig. 2.7).
Chemical Rocks. Assemblages of minerals produced by precipitation from watery solution, either
by organisms or inorganically. Classification is by origin and composition.
(Biogenous)
(Nonbiogenous)
Reef-limestone
Dolomite
Bedded limestone
Evaporite
Chert a )
Coal
Phosphorite
a) Chert denotes a series of rocks ranging from silicified mudstones to very fine-grained quartz rock.
The origin of the silica (quartz) is biogenous opal (at least in Mesozoic and younger rocks).
Metamorphic Rocks. Mineral assemblages produced by defonnation and recrystallization of
igenous rocks or sedimentary rocks through elevated temperature and pressure, with or without
addition of material through injection of solutions. Classification is by degree of foliation, types of
minerals present, and grain size. Metamorphic rocks occur at active margins (see Fig. 2.7).
(Nonfoliated)
Hornfels (from shale, tuff, or lava)
Marble (from limestone or dolomite)
Quartzite (from quartz sandstone)
Amphibolite (from basaltic material or corresp. sediments)
Granulite (from shale, graywacke, or andesite)
(Foliated)
Slate (from shale, tuff)
Schist (from basalt, andesite, tuff, or shale)
Gneiss (from granite, diorite, schist, shale, etc)
Source for A6, any geology text book