Transcript Mineral Characteristics

MINERALS
Characteristics and Properties
Mineral Characteristics
What is a mineral?
• Naturally occurring
• Not man-made (synthetic) or biologically produced.
• Pearls, Styrofoam, charcoal are not minerals
• Inorganic
• Not formed from processes involving organisms (living or once
living)
• Solid
• Has definite chemical composition
• An element or compound
• Has an orderly arrangement of atoms
• Crystalline structure-that is-atoms have repetitive patterns and
internal structures are distinct.
• Geometric solids with smooth surfaces (crystal faces)
Identifying Characteristics of Minerals
– Color
• Color by itself IS NOT sufficient to identify a mineral
– Luster
• How the material reflects light
– Metallic-shiny. Ex: silver, copper, etc
– Nonmetallic-Pearly or vitreous.
– Hardness
• How easily the mineral can be scratched
• Can be compared to the hardness of other minerals by using the Mohs
scale
– Streak
• The powder form of the mineral left on a porcelain plate (must be softer
than the porcelain)
– Cleavage
• The way the mineral splits along flat surfaces
– Determined by the arrangement of the atoms
– Not all minerals have cleavage
– Density
• Ratio of mass to volume
– Determined by the mass of the atoms and how close they are
Formation of Minerals
How are minerals formed?
One way is the cooling of magma
• Thermal energy is lost; atoms migrate together and form different compounds
• The elements present and the amounts determine the kind of minerals
• Different crystal structures are formed
• If the magma cools slowly, large crystals are formed. Different minerals form
at different temperatures. Heavier minerals such as magnetite sink and lighter
ones float.
• Minerals such as quartz and calcite form late in the cooling process and are
known as hydrothermal minerals.
• In the last few years, hydrothermal vents have been formed on the ocean
floor.
• In these areas, sea water filters into the hot crust and is heated to 400
degrees C. The hot water then reacts with the crust and becomes a metal
bearing liquid. When it returns to the cooler sea floor, it deposits minerals,
including iron, copper and zinc sulfide.
Minerals can precipitate out of a solution
• When water is saturated with dissolved solids and can’t hold
• any more, the excess falls out of the solution. An example
• of this is the manganese nodules on the ocean floor
Minerals can form by evaporation
• Minerals such as salt, gypsum and calcite (calcite forms in two ways) are
formed from sea water when it evaporates. This happens in warmer parts of
the world where the sun's heat evaporates the water and leaves the minerals.
Other ways that minerals are formed:
Some minerals are formed from the weathering of rocks.
• Chemical changes are caused by atmospheric oxygen, water and acid rain.
Such action can change feldspars to kaolin and pyrite (fools gold) into a
brown iron ore called limonite
• And lastly some minerals are formed when rocks are metamorphosed, that
is subjected to heat and pressure.
• Minerals formed in this way include garnet and mica.
Mineral Groups
• Minerals that contain oxygen and silicon are called
“silicates”. These two minerals combine to form
most of the minerals in the earth’s crust.
• They are the most abundant single minerals in the
earth’s crust (oxygen-46.6%; silicon-27.7%)
• More than half of the minerals in the earth’s crust
are feldspars which is a silicate
• Some other examples of silicates include: talc,
quartz, mica, topaz, hornblende, garnet, zircon
Uses of Minerals
Gems
• Rarity and beauty makes them valuable
• Gemstones used for jewelry are cut and polished and sometimes don’t resemble the
raw form of the mineral
• May have a crystal structure that allows it to be cut in facets
• May have the addition of another mineral that gives it a brighter color
Ores
• A mineral is an ore if it contains a substance that can be sold for profit
• Hematite is the ore of iron
• Bauxite is the ore of aluminum
• Copper comes from chalcopyrite ore
• Rutile is the ore that titanium comes from
• Titanium is valuable because of its strength and low density (lightness)
• Ore deposits are formed when fluids travel through weaknesses in rocks, such as
fractures and cracks.
• The minerals dissolved in the fluids are left behind when the liquid evaporates,
forming “vein deposits
Mining
• Ores are only profitable if the cost of mining them is less than the value of the
material being mined
• Waste rock has to be removed
• This can be expensive and harmful to the environment
Physical Appearance
• Color cannot be used exclusively to identify minerals. For example
the color of turquoise can vary from blue to green
• Minerals may have varying degrees of transparency, which is the
ability of light to pass through a substance—quartz can be
transparent, but can contain flaws that make it translucent. This is
related to Luster.
• Luster is definitely an identifying physical characteristic
• It describes how light reflects from the surface of the mineral.
Describers might include:
• Metallic, waxy, pearly, earthy, dull,
• glassy (vitreous), silky
Hardness
• This is how easily a mineral can be scratched and is definitely an identifying
characteristics. In order to be scratched by an object, the mineral must be softer
than the object doing the scratching.
• The Mohs scale is a system of comparing the hardness of a list of 10 minerals (The
Giant Cat Found a Foolish Quail that Couldn’t Dance)
• Developed by Frederich Mohs
• It lists them in order from 1 (softest) to 10
• It gives a list of common objects and their hardness
• If the mineral scratches the common object but the object won’t scratch the mineral, the
mineral is the hardest
• Moh's Scale
Streak
• Streak is the color of the powder form of the mineral
• A streak plate is used to do this test. It is a piece of
unglazed porcelain—which has a hardness of 7 on the
Moh’s scale. A streak of the mineral is left on the
porcelain when it is rubbed across with the mineral. The
mineral must be softer than the streak plate if this is to
work.
•
Some minerals leave a certain color streak, which is
an identifying characteristic.
• An example of this is hematite, which although it is a black
mineral, leaves a red streak
Cleavage and Fracture
• When a mineral breaks it does so either by fracturing or by
cleaving. Crystal cleavage is a smooth break producing what
appears to be a flat crystal face.
• Here are a few rules about cleavage. First cleavage is
reproducible, meaning that a crystal can be broken along the
same parallel plane over and over again. All cleavage must
parallel a possible crystal face.
• Fracture describes the way a mineral breaks and is different
from cleavage. A fracture might be splintery, conchoidal (like
glass) , jagged or earthy (like a ball of clay)