Which of these planets…is 1.The seventh planet from the sun? 2.An inner planet? A.Saturn B....
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Transcript of Which of these planets…is 1.The seventh planet from the sun? 2.An inner planet? A.Saturn B....
Which of these planets…is 1. The seventh planet from the sun?
2. An inner planet?
A. Saturn
B. Jupiter
C. Uranus
D. Earth
# 5
P. Reardon 2008 – Based on “Science Starters” by T. Trimpe at http://sciencespot.net/
Let’s Review
What is Atomic Number? Number of Protons in the nucleus.
What is an Isotope? An atom with the same number of protons as its
element but a different number of neutrons.
What are the differences between ionic, covalent, and metallic bonds? Ionic is when atoms transfer electrons and turn into
ions, covalent bonds share electrons, and metallic bonds deal with metals and a “sea of electrons”
Looking Ahead
Tomorrow we start our 2-day lab of mineral identification and properties.
TEST NEXT WEEK! CHAPTERS 1 – 2, PLEASE STUDY!!
Chapter 2.2 & 2.3 Vocabulary
Mineral
Silicate
Silicon-oxygen tetrahedron
Streak
Luster
Crystal Form
Hardness
Mohs Scale
Cleavage
Fracture
Density
PLEASE WRITE DOWN AND DEFINE AS WE GO ALONG!
Introduction
Everything you use and see in life is some sort of combination of minerals. What are some things that you use in your life that
are made of minerals?
Some common examples of mineral use: Pencil lead is made from graphite Body powders use talc Dentist drill bits have small pieces of diamond in
them Quartz in windows
Minerals
A mineral in earth science is NOT the same thing as a mineral in food!
A mineral is a naturally occurring, inorganic solid with an orderly crystalline structure and a definite chemical composition.
For something to be considered a mineral, it must have the following characteristics
Mineral Requirements
Naturally Occurring: Natural geologic processes so synthetic gems do
NOT count as a mineral!
Solid Substance: Minerals must be solid at temperatures that are
normal at Earth’s surface.
Orderly Crystalline Structure: Atoms/ions are arranged in orderly and repetitive
manners. Opal is not a mineral!
Mineral Requirements
Definite Chemical Composition: Most minerals are chemical compounds made of
two or more elements. A few only have one element.
Generally considered inorganic: Inorganic crystalline solids found in nature. Salt
(halite) is a mineral, but SUGAR IS NOT because SUGAR IS ORGANIC (comes from sugar cane—a plant).
“Generally Organic” because sometimes animals (especially in oceans) secrete calcium carbonate from their shells and this is considered a mineral.
How Minerals Form
Form everywhere on earth under very different conditions.
Silicates form deep in the crust or mantle where pressures and temperatures are VERY HIGH.
Minerals known as carbonates form in warm, shallow ocean water.
Clay minerals form at Earth’s surface when existing minerals are exposed to weathering.
Others form when rock is exposed to pressure or temperature changes.
How Minerals Form
Four major processes by which minerals form: Crystallization from Magma Precipitation Changes in pressure and
temperature Formation from hydrothermal
solutions
Crystallization from Magma
Magma is molten rock.
Formed deep within the earth.
As magma cools, elements combine to form minerals. First to form are minerals rich
in iron, calcium, and magnesium.
As minerals continue to form, the composition of the magma changes. Minerals rich in sodium,
potassium, and aluminum form.
Precipitation
Water in Earth’s lakes, rivers, ponds, oceans, and beneath its surface contains many dissolved substances.
When water evaporates, these substances can react to form minerals.
Changes in temperature can also cause minerals to precipitate out of water.
Precipitation means that it is left behind—drops out of solution. Halite (salt) and limestone!
Pressure and Temperature
Some minerals (including talc and muscovite) form when existing minerals are subjected to changes in pressure and temperature.
Pressure increase can cause minerals to recrystallize while still solid. Atoms simply rearrange.
Changes in temperature can make minerals unstable. New minerals form.
Hydrothermal Solutions
Hydrothermal solutions are very hot mixtures of water and dissolved substances. Temperatures between 100
and 300 degrees Celsius.
When solutions come into contact with other minerals chemical reactions happen that form NEW minerals.
Solutions cooling causes new minerals to form like quartz and pyrite.
Introduction
Over 3800 minerals have been named, and new ones are identified each year. We only study the most abundant minerals in this
class.
Common minerals, together with thousands of others that form on Earth, can be classified into groups based on their Composition.
Silicates
Two most abundant elements in Earth’s crust are oxygen and silicon.
Silicon and Oxygen combine to form a structure called the silicon-oxygen tetrahedron. One silicon atom and 4
oxygen atoms. Framework for EVERY
SILICATE mineral.
Most silicates also contain other elements (except for pure quartz).
Silicates
The tetrahedra can join in a variety of ways.
Very strong bonds.
Olivine is made of millions of single tetrahedra. Augite has the
tetrahedra form chains.
Double chains of tetrahedra form in minerals like hornblende.
Provide clues about the conditions the mineral formed in.
Most silicates crystallize from magma as it cools.
Can form at the surface or deep underground. Place of formation and
chemical composition influence which silicates form.
Olivine crystallizes at 1200 degrees C, but quartz crystallizes at 700 degrees.
Clay minerals from from silicates exposed to weathering at the surface.
Carbonates
Second most common mineral group.
Carbonates are minerals that contain the elements carbon, oxygen, and one or more other metallic elements.
Calcite (CaCO3) is the most common carbonate mineral. Dolomite contains
magnesium and calcium.
Both limestone and marble are rocks composed of carbonate materials. Used in building in
construction.
Oxides
Minerals that contain oxygen and one or more other elements, which are usually metals.
Some form as magma cools beneath Earth’s surface.
Others (like corundum) form when existing minerals are subjected to changes in temperature and pressure.
Corundum is an aluminum oxide.
Hematite forms when existing minerals are exposed to liquid water or to moisture in the air. Hematite is one form
of iron oxide.
Sulfates and Sulfides
Minerals that contain the element sulfur.
Sulfates form when mineral-rich waters evaporate and leave the minerals behind. Gypsum Anydrite
Sulfides form from thermal (hot-water) solutions. Galena Sphalerite Pyrite
Halides
Minerals that contain halogen ions plus one or more other elements.
Halogens are elements from group 7A of the periodic table. Fluorine, Chlorine
Halite (NaCl) is a common halide.
Fluorite (CaF2) is also common and used in making steel. Forms when salt water
evaporates.
Native Elements
Group of minerals that exist in relatively pure form. Gold (Au) Silver (Ag) Copper (Cu) Sulfur (S) Carbon (C)
Native forms of carbon are diamonds and graphite.
Form in hydrothermal solutions. Gold Rush TV Show
Introduction
Minerals come in many different sizes, shapes, and colors.
Some minerals are harder to break than others, some reflect light differently, and some have different textures.
There are several different ways to identify and classify different minerals.
By Color One of the first things you
usually notice about a mineral.
Color is unique to certain minerals so this property is sometimes useful in mineral identification.
Small amounts of different elements can give the SAME MINERAL different colors. Sapphires vs. Rubies
Even though color CAN BE USEFUL, it is not something that you can rely on by itself! Color can sometimes be misleading! Pyrite vs. Gold
By Streak
Streak is the color of a mineral in its powdered form.
Obtained by rubbing a mineral across a streak plate.
Color may vary between mineral samples, but the STREAK WILL NOT!
Help see the difference between metallic and nonmetallic minerals. Metallic minerals have dark,
dense streaks. Nonmetallic minerals do not
have such streaks.
By Luster
Luster is used to describe how light is reflected from the surface of a mineral.
Minerals that have the appearance of a metal—regardless of their color—are said to have a metallic luster.
Nonmetallic lusters include: Vitreous Glassy Pearly Silky Earthy Adamantine Sub-Metallic
By Crystal Form
Crystal form is the visible expression of a mineral’s internal arrangement of atoms.
Every mineral has a distinct crystal form.
When a mineral forms slowly and without space restrictions it will develop into a crystal with well formed faces—sides, top, and bottom. But usually minerals
form in cramped, smashed spaces and intergroup so you cannot see their crystal form easily.
By Hardness
One of the most useful properties to identify a mineral.
Hardness is a measure of the resistance of a mineral to being scratched. This can be determined by rubbing the mineral
against another mineral of known hardness—one will scratch the other unless they have the same hardness.
Geologists use a standard hardness scale called the Mohs Scale. The Mohs scale consists of 10 minerals arranged
from 10 (hardest) to 1 (softest).
By Hardness
Other objects can also be used to determine hardness. Your fingernail has a hardness of about 2.5 Copper Penny has a hardness of about 3.5 Glass has a hardness of 5.5
So the mineral Gypsum, which has a hardness of 2, can be scratched by your fingernail! Quartz has a hardness of 7, so it will scratch glass! Diamond is the hardest mineral on Earth and can
scratch anything (Mohls Level 10)
By Cleavage
In the atomic structure of a mineral, some bonds are weaker than others. These weak bonds are paces where a mineral will break when
it is stressed.
Cleavage is the tendency of a mineral to cleave, or break, along flat even surfaces.
Micas have the simplest cleavage—since they are weak in one direction they tend to cleave in flat sheets
Quartz has strong bonds in all directions, so it does not have cleavage but FRACTURES instead. Cleavage can happen in more than one direction at a time;
Halite has 3 cleavage directions!
By Fracture
NOT the same thing as cleavage.
Minerals that DO NOT show cleavage when broken are said to fracture.
Fracture is the uneven breakage of a mineral. If minerals tend to break into smooth curves
surfaces, they are said to have conchoidal fracture. Fibrous Fracture Irregular Fracture
By Density
Density is a property of all matter that is the ratio of an object’s mass to its volume. D = m/v
Density of copper is 8.96 g/cm3
So any sample of copper will have that density.
Most minerals will have a density between 2 and 5 g/cm3
The density of a mineral is a COMMON VALUE and is therefore a good indicator of mineral identity. Density tables will be given on tests, don’t feel like
you have to memorize them all!
By Distinctive Properties of Minerals
Some minerals can be recognized by other distinctive properties. Talc and Graphite have distinctive ‘feels’.
Talc is ‘soapy’ Graphite is ‘greasy’
Metallic minerals are easily shaped (think copper, gold, etc!)
Magnetite is magnetic!
Calcite will double print when you look through it! This is called double refraction.
Sulfur’s streak smells like rotten eggs.
Carbonate minerals fizz when exposed to Hydrochloric Acid
Mineral Properties depend on the elements that compose the mineral (it’s composition) and its structure (how its atoms are arranged).
Let’s Review
What is a native element? A group of minerals that exist in a relatively pure form.
What are the four ways minerals form? From cooling magma, from changes in temperature and
pressure, precipitating, and from hydrothermal solutions.
What is luster? How light is reflected from the surface of a mineral.
Why is color a bad indicator for identifying a mineral? Color is unique to some minerals, but often it is hard to
distinguish on color alone.