abrasion
-is the wearing away of a material by
objects rubbing against each other.
A horizon
-is also known as either top soil or the zone of leaching.
Typically it is dark colored because of
the humus (organic materials). Decomposed materials are washed out of this layer, a process
known as
leaching. -soil
layers-Opal's Pals
angular grain
-is an unweathered grain, often with an
irregular shape and sharp edges. -angular
grains-Opal's Pals
bauxite
-is the ore of aluminum, hydrated alumina.
Bauxite often has a pisolitic structure (made of small
rounded aggregates).
B horizon
--is the second layer of soil. It is also known as the zone of
accumulation because materials
washed down from the top layer, clay and iron
oxides, accumulate in this layer. -soil
layers-Opal's Pals
boulder
-is a particle size larger than a cobble;
there is no upper limit established as to how large a
boulder can be.
-is a soil cemented by lime (calcite);
caliche is very common in the Southwest. Caliche closely
resembles concrete.
-caliche:
12 -caliche-Opal's
Pals
carbonic acid
-consists carbonated water; carbonic acid is
a weak acid made of carbon dioxide and water.
Carbonic acid can eventually
cause the decomposition of most silicate minerals.
chemical weathering
-occurs when a mineral is changed into a
different mineral through the process of a chemical
reaction; the new mineral is
usually less resistant to further weathering.
-can either refer to the tiniest particle
size (submicroscopic particles) or it can apply to a class of
silicate minerals
that only produce crystals in the submicroscopic range (clay minerals).
-is the particle size between a pebble and a
boulder. A cobble is often described as "brick-sized".
devitrification of obsidian
-Like all glasses in which the constituent
atoms are arranged at random, obsidian breaks down as
it slowly crystallizes
over thousands or even millions of years.
-pitchstone is obsidian undergoing devitrification.
differential weathering
*due to differences in hardness, toughness,
types of cementation, and chemical composition, some
rock types break down
(weather) faster than other materials.
-is the process of dissolving a material;
the material goes into solution.
erosion
-is the process of carrying away materials
in contrast to weathering which causes the breakdown
of materials.
exfoliation
-is a weathering process, common in semiarid
regions, in which the weathered outer portion of a
granite boulder peels off in
slabs parallel to the surface of the boulder. This weathering process is
often
compared to the layers of an onion.
-Water gets into a crack, freezes, and
expands; the tremendous pressures exerted by the expansion
of water into ice can
cause the rock to split further. -Frost
wedging of thin-bedded siltstone
grus
-is a pile of small fragments from a
decomposed granite. This loose material contains single grains
of quartz, mica,
and weathered feldspar as well as small clumps of these minerals.
-is a chemical reaction in which water is
added to the chemical formula of a mineral: the addition
of water to the mineral
anhydrite changes its chemical composition and the material becomes
gypsum.
-anhydrite -gypsum
hydrothermal alteration
-occurs when hot mineralized water coming
from an igneous intrusion changes the composition
and structure of the minerals
in the surrounding country rock.
oxidation
-occurs when a mineral picks up extra oxygen in its structure a changes to a new
mineral.
As an example, magnetite in basalt is altered to a red hematite. -red soil in Maui, Hawaii
pedalfer
-is a soil formed in warm humid regions,
rich in iron oxides (red) and clay (gooey).
pedocal
-is a soil found in semiarid regions, rich
in calcite.
physical weathering
-is the breakdown of rocks into smaller
pieces without any change in chemistry; also called
mechanical weathering.
regolith
-is the loose material on top of bedrock:
soil, gravel, boulders, etc.
rock flour
-consists of rock that has been crushed and
ground to a fine powder by glacial action.
root wedging
-Roots grow to a thin crack in a rock; as
the root grows it exerts pressure and expands the crack.
-is the buildup of salt in the soil thereby
decreasing the useful of the soil for agriculture; a growing
problem in the
western part of the United States.
salt buildup
-If there is insufficient drainage of
agricultural watering of crops, salt (which is produced by the
breakdown of soil
minerals) is not washed out of the system. Consequently, the concentration of
salt slowly builds up until plants cannot live in the soil.
salt wedging
-is a physical weathering process similar to
frost wedging but instead is caused by the growth of
salt crystals within
cracks. The force of the growing salt crystal is sufficient to widen cracks in
rocks.
-refers to sets of joints in bedrock that
are produced by unloading; the joints produced by this
process are usually
parallel to the surface of the Earth.
-is a particle size larger than clay
particles but smaller than sand grains. This material feels gritty
but you
cannot see the individual particles with the naked eye.
-Chemical weathering within fractures in
rock first causes a breakdown of the corners of the block
and then edges of the
block are also destroyed, thus producing a rounded boulder from an angular
block.
-spheroidal weathering:
1
2
3
talus
-consists of loose rock that
has slid down a slope.
-occurs when most materials are heated.
Similarly, most materials contract in size when cooled.
Repeated heat-cold
cycles loosen grains within rocks and may cause the rock to eventually
crumble.
ultraviolet light
-refers to the frequencies of light just
outside of the normal visible spectrum, just past violet.
This type of light is
responsible for sunburn on bright, sunny days. Ultraviolet light can cause
chemical changes in minerals; many colored minerals such as amethyst, rose
quartz, and pink
topaz can fade when exposed to ultraviolet light. -minerals that
fluoresce under ultraviolet light
unloading
-occurs when the pressure is reduced of a
rock that formed under pressure, the rock expands and
breaks. Granite
intrusions formed at depth crack and split when the overlying bedrock is removed
through erosion. -jointing in an granite intrusion
varve
-is a thin layer of silt or clay deposited on the bottom of a lake bed on an
annual basis.
Sediment varies slightly from winter to summer, producing
small distinguishable layers. -varves
wave action
-is mechanical weathering force capable of
breaking and rounding rock fragments through
constant abrasion.
-is the breakdown of rocks and minerals by
chemical and physical processes..
weathering rind
-is the outer part of a rock when exposed to
weathering process often changes color; this is why a
rock must be broken in
order to see a fresh surface.
Chapter 5-Weathering and Soils 