Re: [Geology2] How to Identify the 3 Major Types of Rocks

--------------------------------------------
On Tue, 12/19/17, 'allison.ann' allison.ann@att.net [geology2] <geology2@yahoogroups.com> wrote:

Subject: Re: [Geology2] How to Identify the 3 Major Types of Rocks
To: geology2@yahoogroups.com
Date: Tuesday, December 19, 2017, 3:44 PM


 









Nice..Thank you! 


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-------- Original
message --------From: "Kim Noyes
kimnoyes@gmail.com [geology2]"
<geology2@yahoogroups.com> Date: 12/17/17
11:44 PM (GMT-06:00) To: CentralCoastRockhounds
<centralcoastrockhounds@yahoogroups.com>, Geology2
<geology2@yahoogroups.com> Subject:
[Geology2] How to Identify the 3 Major Types of Rocks


 













How to Identify the 3 Major
Types of Rocks - ThoughtCo

www.thoughtco.com

Using pictures of rocks is a simple way to help you identify
unknown samples. Read about the three major rock types and
characteristics of each.

How to Identify
the 3 Major Types of Rocks












by
Staff Author









Updated December 11, 2017















In geology,
pictures of rocks can be used to help you best determine
which of the
three major types a particular rock belongs to: igneous,
sedimentary, or
metamorphic.By comparing your rock sample with
photographic
examples, you can identify key characteristics such as how
the rock was
formed, what minerals and other materials it contains, and
where the
rock may have come from.Sooner or later, you're
bound to
encounter hard, rock-like substances that aren't
actually rocks. Such
items include man-made substances like concrete and bricks,
as well as
rocks from outer space (such as meteorites) that have
dubious origins.Before
beginning the identification process, make sure that your
sample has
been washed to remove dirt. You'll also want to make
sure you have a
freshly cut surface so you can identify color, grain
structure,
stratification, texture, and other characteristics.
Igneous
Rocks
Igneous rocks are created by
volcanic activity and form as magma and
lava cool and harden. They are most often black, gray, or
white in
color, and often have a baked appearance. As they cool,
these rocks may
form crystalline structures, giving them a granular
appearance; if no
crystals form, the result will be natural glass. Examples of
common
igneous rocks include:Basalt:
Formed from low-silica lava, basalt is the most common type
of volcanic
rock. It has a fine grain structure and is usually black to
gray in
color.Granite:
This igneous rock may range from white to pink to gray,
depending on
the mix of quartz, feldspar, and other minerals it contains.
It is among
the most abundant rocks on the planet.Obsidian:
This is formed when high-silica lava cools rapidly, forming
volcanic
glass. It is usually glossy black in color, hard, and
brittle.

More
»

Sedimentary
Rocks
Sedimentary rocks, also called
stratified rocks, are formed over time
by wind, rain, and glacial formations. They may be formed
by erosion,
compression, or dissolution. Sedimentary rocks may range
from green to
gray, or red to brown, depending on their iron content, and
are usually
softer than igneous rocks. Examples of common sedimentary
rocks include:Bauxite:
Usually found at or near the earth's surface, this
sedimentary rock is
used in the production of aluminum. It ranges from red to
brown with a
large grain structure.Limestone:
Formed by
dissolved calcite, this grainy rock often contains fossils
from the
ocean because it is formed by layers of dead coral and other
marine
creatures. It ranges from cream to gray to green in
color.Halite: More commonly known as
rock salt, this sedimentary rock is formed from dissolved
sodium chloride, which forms large crystals.

More
»

Metamorphic
Rocks

Metamorphic
rock formations occur when sedimentary and igneous
rocks become
changed, or metamorphosed, by conditions underground. The
four main
agents that metamorphose rocks are heat, pressure, fluids,
and strain.
These agents can act and interact in an almost infinite
variety of ways.
Most of the thousands of rare minerals known to science
occur in
metamorphic rocks. Common examples of metamorphic rocks
include: Marble: This
coarse-grained, metamorphosed limestone ranges in color
from white to
gray to pink. The colored bands (called veins) that give
marble its
characteristic swirled appearance are caused by mineral
impurities.Phyllite:
This shiny, colorful metamorphosed slate ranges in color
from black to
green-gray. It can be recognized by the flakes of mica that
it contains.Serpentinite: This
green, scaly rock is formed beneath the ocean as sediment is
transformed by heat and pressure. 

More
»










Other Rocks and Rock-Like Objects


Just because a sample looks like a rock
doesn't mean it
is one, however. Here are a few of the most common that
geologists
encounter:

Meteorites are (usually) small,
rock-like formations
originally from outer space that survived the trip to
earth. Some
meteorites contain rocky material in addition to elements
like iron and
nickel, while others are comprised solely of mineral
compounds.

Concretions resemble smooth, often
oblong masses
found along a riverbed, apparently cemented together. These
are not
rocks, but masses formed by dirt, minerals, and other
water-borne
debris.

Fulgurites are hard, jagged, oblong
masses are formed from soil, rock, and/or sand that has been
fused together by a lightning strike.

Geodes are sedimentary or metamorphic
rocks that contain a hollow, mineral-filled interior like
quartz.

Thundereggs are solid, agate-filled
lumps found in volcanic regions. They resemble geodes with
opened.

Nearly 30 US states have official state rocks, ranging
from marble in Alabama to red granite in Wisconsin.




























--

 






 
Kim Noyes
about.me/kim.noyes




















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Posted by: Lizeth Karr <lizethkarr@yahoo.com>
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