matter and minerals. elements and the periodic table matter elements are the basic building blocks...
TRANSCRIPT
Elements and the Periodic Table
Matter
Elements are the basic building blocks of minerals.
Over 100 elements are known.
Atoms
Smallest particles of matter
Matter
Have all the characteristics of an element
• neutrons, which have neutral electrical charges
The nucleus is the central part of an atom and contains• protons, which have positive electrical charges
Atoms
Matter
Energy levels, or shells• surround the nucleus• contain electrons—negatively charged particles
The atomic number is the number of protons in the nucleus of an atom.
Isotopes
Many isotopes are radioactive and emit energy and particles.
Isotopes of an element have the same number of protons but varying numbers of neutrons.
Have different mass numbers: the sum of the
neutrons plus protons
Matter
The mass number is the number of neutrons and protons in the nucleus of an atom.
Why Atoms Bond
• A compound consists of two or more elements that are chemically combined in specific proportions.
When an atom’s outermost energy level does not contain the maximum number of electrons, the atom is likely to form a chemical bond with one or more atoms.
Matter
• An ion is an atom that gains or losses electrons.
Types of Chemical Bonds 1. Ionic bonds form between positive and
negative ions.
Matter
2. Covalent bonds form when atoms share electrons.
3. Metallic bonds form when metal ions share electrons.
Minerals: the building blocks of rocks
• Definition of a Mineral: naturally occurring inorganic solid characteristic crystalline structure definite chemical composition
How do we identify minerals?
• Physical properties: Color Luster Hardness Crystal shape Cleavage Specific gravity Other
Physical Properties of Minerals
• Color:– Most obvious, but often misleading– Different colors may result from impurities
Example:Quartz
Physical Properties of Minerals
• Color: Streak – color of a mineral in powdered form
(used for metallic minerals)
Obtained by scratching a mineral on a piece of unglazed porcelain.
Example:Hematite
Streak• Red chalk on a chalk board
makes red marks. White chalk makes white marks.
• Not all minerals work this way. When some minerals are scratched along a ceramic streak plate, it creates a different color.
Pyrite or “Fool’s Gold”• When pyrite is run
across a streak plate, it has a black or dark green streak.
• Pyrite is not worth much money, while gold is worth a lot. They look alike, so miners call it fool’s gold.
Hematite• Hematite’s color is
grey, but its streak is red.
• Hema means blood.
• The mineral was named hematite because it looked like it was bleeding when it was taken across a streak plate.
Physical Properties of Minerals
• Luster:– How a mineral surface reflects light– Two major types:
• Metallic luster• Non-metallic luster
Metallicexample:Galena
Non-metallicexample:
Orthoclase
Physical Properties of Minerals
• Hardness:– How easy it is to scratch a mineral– Mohs Scale of Hardness
• relative scale• consists of 10 minerals, ranked 1 (softest)
to 10 (hardest)
Mohs Scale of Hardness
Hardest (10) – Diamond
Softest (1) – Talc
Common objects:
- Fingernail (2.5) - Copper penny (3.5) - Wire nail (4.5) - Glass (5.5) - Streak plate (6.5)
Hardness• Is measured by how easy it is to
scratch. • Geologists order the hardness
by…1. Scratched by a fingernail.2. Scratched by a penny. 3. Scratched by a nail. 4. Scratched by a diamond.
These are not all of the tools geologists use, but it will work for
our experiment.
Calcite is soft, but a little harder because it cannot be
scratched by a fingernail, but it can be scratched by a penny.
Physical Properties of Minerals
• Crystal shape (or form):– external expression of a mineral’s internal
atomic structure– planar surfaces are called crystal faces– angles between crystal faces are constant for
any particular mineral
Quartz Pyrite
Physical Properties of Minerals
• Cleavage vs. Fracture:– The way a mineral breaks
– Cleavage: tendency of a mineral to break along planes of weakness
– Minerals that do not exhibit cleavage are said to fracture
Do not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when the mineral is broken.
Physical Properties of Minerals
• Cleavage is described by:– Number of planes– Angles between adjacent planes
– These are constant for a particular mineral
Physical Properties of Minerals
• Fracture:– minerals that do not exhibit cleavage are said to
fracture
– smooth, curved surfaces when minerals break in a glass-like manner: conchoidal fracture
Quartz
Physical Properties of Minerals
• Specific gravity:– weight of a mineral divided by weight of an
equal volume of water– metallic minerals tend to have higher specific
gravity than non-metallic minerals
GalenaSG=7.5
QuartzSG=2.67
– reaction with hydrochloric acid (calcite fizzes)
Physical Properties of Minerals
• Other properties:
– taste (halite tastes salty)
– feel (talc feels soapy, graphite feels greasy)
– magnetism (magnetite attracts a magnet)
• Rock-forming minerals– ~30 common minerals make up most rocks in
Earth’s crust– Composed mainly of the 8 elements that
make up over 98% of the crust
Mineral Groups
Mineral Groups
All others: 1.5%
Element Abundances
Silica(SiO4)4-SILICATES
Common cations thatbond with silica anions
– Oxides O2-
– Carbonates (CO3)2-
– Sulfides S2-
– Sulfates (SO4)2-
– Halides Cl-, F-, Br-
– Native elements (single elements; e.g., Au)
Mineral Groups
• Silicates (most abundant)
• Non-silicates (~8% of Earth’s crust)
Mineral Groups
FerromagnesianSilicates (Fe, Mg)
Non-ferromagnesianSilicates (K, Na, Ca, Al)
OxidesCarbonatesSulfides/sulfatesNative elements
Mineral Groups – Silicates
1. Silicates– Tetrahedron
• fundamental building block
• 4 oxygen ions surrounding a much smaller silicon ion
Silicon-oxygentetrahedron
(SiO4)4-
Mineral Groups – Silicates
• Joining Silicate Structures
– How tetrahedra may be linked:• independent tetrahedra
• single chains
• double chains
• sheets
• 3-D framework
Pyroxene GroupFerromagnesian / dark silicates (Fe-Mg)
Mineral Groups – Silicates
2-directionsof cleavage(at nearly 90 degrees)
Augite
Amphibole GroupFerromagnesian / dark silicates (Ca, Fe-Mg)
Mineral Groups – Silicates
2-directionsof cleavage(not at 90 degrees)
Hornblende
Mica Group and Clay Mineralslight silicates (K, Al)
Mineral Groups – Silicates
1-directionof cleavage
Muscovite
non-ferromagnesian
Feldspar Grouplight silicates (K-Na-Ca, Al)
Mineral Groups – Silicates
2-directionsof cleavage
(at 90 degrees)
Orthoclase
Plagioclase
K-feldspar
Ca/Na-feldspar
Most common mineral group
Quartzlight silicates (pure SiO2)
Mineral Groups – Silicates
no cleavage(conchoidal fracture)
hard, resistant to weatheringQuartz
Mineral Groups
Minerals
2. Carbonates• Minerals that contain the elements carbon,
oxygen, and one or more other metallic elements
3. Oxides• Minerals that contain oxygen and one or more
other elements, which are usually metals
Mineral Groups
Minerals
4. Sulfates and Sulfides• Minerals that contain the element sulfur
5. Halides• Minerals that contain a halogen ion plus one or
more other elements
6. Native elements• Minerals that exist in relatively pure form