Rocks
 What is a rock?
Naturally occurring, solid.
 How many minerals do you need in a rock?
Most rocks have a variety of minerals but obsidian and coal have none.
 How do geologists categorize rocks?
In various ways but one important way is the way they form.
Sedimentary through erosion, deposition, and cementation. Pressure pushes loose
sediment together into a rock.
Igneous molten material cools on or in Earth.
Metamorhic rocks are heated and pressured additionally.
Igneous rocks can be intrusive (formed in the earth) or extrusive (formed on the
earth) Which has more visible crystals? Intrusive because it has more time to get
with its friends and form a group. Extrusive is like a fire drill. Everyone is just
going out of the building and there is not time to find friends.
Metamorphic rocks can be foliated or non foliated. Foliated (neat folded laundry)
has visible lines that show how the rock was pressed down GNEISS OR SLATE.
Non foliated just looks normal with no parallel lines QUARTZITE OR
MARBLE.
Know how each rock can become the other rock.
What is a sedimentary rock and how do they form?
 Sedimentary rocks form by the weathering and erosion of preexisting rocks or
from the deposition of organic material.
 When preexisting rocks are exposed at the surface they are subjected to chemical
and mechanical weathering, which breaks them down into small pieces called
sediment.
 The sediment is then transported by ice, water, or wind to another location where
it is deposited, commonly in horizontal layers or strata. Compaction occurs as
more and more sediment is deposited. In many cases, dissolved minerals
recrystallize and cement the sediments together as well. When compaction and
cementation change the sediment into rock, lithification occurs.
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There are three major types of sedimentary rock—clastic, chemical, and organic.
A clast is a piece of rock or the hard part of an organism, such as a shell or bone.
Thus, when clasts are compacted or cemented together, they form clastic
sedimentary rock.
Chemical sedimentary rock forms when dissolved minerals or organic materials
recrystallized out of a water solution. One example of a chemical sedimentary
rock is chemical limestone, which forms at the bottom of the ocean. Another is
rock gypsum, which forms as water evaporates from shallow lakes.
Organic sedimentary rock forms from the depositing of large amounts of organic
material, as occurs in areas such as swamps.
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Rock notes - Fort Thomas Independent Schools