1.1/2/3. (8/26-30) Minerals & Weathering (origins of sediment) Flashcards
What is Bowen’s Reaction Series?
If we look at the major rock forming minerals, this is the order in which they form
What is the order for Bowen’s reaction series?
- Olivine, calcium-rich feldspar
- pyroxenes, amphiboles, sodium-rich feldspar
- biotite mica, muscovite mica, potassium-feldspar, quartz
What is the order dependent on?
temperatures
How do these minerals form?
- deep in the earth with a melt/magma/liquid
- they crystalize as the cool off
What is the temperature range?
1000-600 centigrade
What do the temperatures mean for the minerals?
600- in balance with the conditions at the surface
1000- out of wack
(Bowen’s reaction series) What kind of rocks are formed?
- basalts: olivine, pyroxenes, dark in color, coming out of Hawaii
- -
Which will weather first?
backwards in the sense that the mineral that is formed first goes first
Are all beaches made of quartz?
no, coquina beaches are composed of coral, shells, and pellets (fecal matter)
What are the two kinds of sand factories?
- land: clastic sediment (decomposed rock)
- ocean: (bio)chemical sediment- biologic material that gets broken up
In the (bio)chemical process, which mineral is involved to make chemical sedimentary rock?
calcite CaCo3 in the ocean
What are clastic/siliciclastic sediments?
Minerals that contain silica SiO2:
quartz, feldspar, hornblende, etc.
What is sediment texture?
How we describe rocks/sediments
includes:
grain size, sorting, shape, and support
What is grain size?
Part of sediment texture
*Applies to clastic sediments: a way to categorize individual minerals in a rock
*>2mm- gravel, pebbles, cobbles
*2mm-0.063mm- sand
*0.004mm- silt
*<0.004mm- clay
*Very coarse-> coarse-> medium-> fine-> very fine
What is sorting?
Part of sediment texture
- ranges in grain size
- various grain sizes
well sorted -> poorly sorted
What is grain shape?
Part of sediment texture
- angular -> rounded
What is support?
Part of sediment texture
- matrix vs. grain supported
- sediments can touch each other (grain)
- sediment can also not touch (matrix)
- chemically bound
How do we know the maturity of a sediment?
mature: rounded, well sorted
immature: angular, poorly sorted
What are the three components of a sedimentary rock?
- grain (can touch, sand)
- matrix (smaller stuff in between, silt, finer grain)
- cement (glued together, iron oxide, silica, calcium carbonate, etc)
What are the weathering processes?
- Chemical
- Physically, mechanical
- both
What is exfoliation?
mechanical weathering
like peeling an onion
when the granite’s confining stress and pressure gets released as it surfaces, it expands
Why does a puzzle rock break apart?
thermal weathering
temperature extremes cause thermal expansion and contraction which cause a rock to fall apart
How do dry areas affect rocks?
- If salt gets into the cracks it degrades it
- they are corrosive
- they also expand and contract
How does the cold affect rocks?
When water freezes it expands breaking a rock apart if it gets in its cracks
What are examples of mechanical weathering?
rainfall and temperature and roots (biological activity) and fires, freeze thaw
What are the four major chemical processes?
- solution
- redox
- hydrolysis
- chelation
What is saprolite?
Decomposed rock/ sand
What are core stones?
partially decomposed rock
What is the weathering front?
the contact between the solid rock and where it is being decomposed
What is soil?
where the saprolite is organized into horizons
What is granite?
A typical mineralogically homogeneous igneous rock composed of quartz, feldspar, and hornblende
What is a corestone?
The unweathered core of a weathering interface created by weathering proceeding rapidly along joint and fractures that easily transmit water.
What are chelators?
Organic acids that are able to complex insoluble cations like iron and aluminum
What is physical weathering?
the mechanical breakdown of rock into smaller pieces
What is chemical weathering?
the chemical transformation of minerals in rock, typically with the loss of mass
What are the main master horizons in a soil?
A, B, and C
What is sand?
Any detrital material (sediment) that falls between 0.064 and 2 mm in diameter
What is the material that creates isovolumetric chemical weathering of rock called?
saprolite
Why does the study of sediment and sedimentary rocks care about rock weathering and soils?
weathering and soils generate clastic detritus that will eventually become new sedimentary rocks
How is soil developed?
climate, organisms, relief, parent material, and time
