sedimentary rocks - carleton collegedmaxbauer/sedimentary_rocks_tutorial.… · calcite and...
TRANSCRIPT
SEDIMENTARY ROCKSSedimentary rocks form through the accumulation of sediments - which can be both clastic (bits of other rocks) or chemical (mineral grains that precipitate out of surface waters). All sediments form through process-es we can generally classify as ‘weathering’ processes. We will spend a good amount of our class thinking about sedimentary rocks and associated topics. For now, focus on using the information below to get yourself familiar with some common sedimentary rocks and minerals.
Clastic (Detrital)
Sedimentary Rocks
Chemical (Biochemical)Sedimentary
Rocks
Grain Size Typical Minerals Rock Name
Mineralogy Rock Name
Coarse Grained (> 2 mm)
Medium Grained (1/16 - 2 mm)
Fine Grained (< 1/16 mm)
quartz, feldspars, pieces of other rocks (lithics)
pieces of other rocks (boulders, cobbles,
pebbles) + sand
clay minerals, quartz
Conglomerate or Breccia
Sandstone
Shale
calcite
dolomite
halite
gypsum
microcrystalline quartz
limestone
dolostone
rock salt
rock gypsum
dolostone
TABLE 1. CLASSIFICATION OF COMMON SEDIMENTARY ROCKS
KEY TERMS AND CONCEPTS:The term ‘clastic’ comes from siliciclastic - and refers primarily to the mineralogy. Siliciclastic rocks are named and differentiatied by grain size, as you see above. Grain size varies within each clastic category shown above - so when we talk about sandstones sometime we will say “coarse-grained” or “fine-grained” as a modifier to describe the sand grains.
Calcite and dolomite are both carbonate minerals, so we will talk about them broadly in the sense of carbon-ate sedimentary rocks, which includes both limestone and dolostone.
Cementation: To turn sediment into a sedimentary rock you need minerals to precipitation out of the waters within pore spaces between adjacent grains of sediment. The minerals that precipitate are called ‘cement’. Common cements include carbonate minerals, quartz, and sometimes iron oxides (hematite).