Notes: Ch5 – What is a Mineral?
Minerals are mined from the Earth’s crust.
• There are over 4000 known minerals.
• 8 elements make up most of them.
• The most abundant minerals are made from Silicon & Oxygen.
• Most minerals are compounds – a combination of two or
more elements.
Ex: Quartz – Si & O
• Some minerals consist of a single element which are called native elements or native
minerals.
Ex: Silver (Ag), Copper (Cu)
• Minerals like mica, quartz, feldspar and calcite are often found mixed together into
something called a ROCK . So, those minerals are known as Rock-Forming Minerals.
Mineral - A naturally occurring inorganic solid with a distinct chemical composition and
crystalline structure -- Broken down into 5 Rules!
1. Occurs Naturally
• Minerals are found in the earth in dirt, rocks, and water.
• They are not made by man.
2. Inorganic
 They are not alive. No plants or animals.
 Not derived from a plant or an animal.
3. Solid
• Anything that is a liquid or gas is not considered a mineral.
*Remember….
S – solid
O – orderly
N – natural
I – inorganic
C –chemical
4. Definite Chemical Composition
• Minerals always have the same chemical makeup.
• Ex: Quartz will always consist of one part Si and two parts O.
5. Atoms arranged in an orderly pattern.
• Most often seen through a minerals crystal shape.
• A crystal is a regular geometric solid with smooth surfaces called crystal faces.
• If space is limited when a mineral is forming, there may not be enough room for crystal
faces to fully develop or “grow.”
Crystals
 A mineral’s crystal shape and hardness are determined by the arrangement of atoms.
The 6 Basic Crystal Shapes
Cubic
 3 equal-length axes of symmetry
 All 90° angles
 Halite / Pyrite
Orthorhombic
 3 unequal axes of symmetry
 All 90° angles
 Topaz
Tetragonal
 3 axes of symmetry: 2 same length,
one different
 All 90 ° angles
 Zircon
Monoclinic
 3 unequal axes of symmetry
 Two at 90° angles, one not
 Gypsum / Calcite
Hexagonal
 4 axes of symmetry
 3 same length at 120° angle
 1 different length at 90° angle
 Quartz
Triclinic
 3 unequal axes of symmetry
 No 90 ° angles
 Feldspar
GEMSTONES are mineral crystals that are cut and polished and used to make
jewelry.
3 Ways that Minerals Form
1. From the cooling of molten rock (magma/lava).
2. From evaporation or precipitation out of liquids.
Ex: Water evaporates and leaves minerals behind.
3. Existing minerals are transformed by extreme heat & pressure.
NOTES: CH 5 – HOW CAN WE IDENTIFY MINERALS?
MINERAL PROPERTIES
To identify a mineral, we look at their different properties such as…Color, Luster,
Streak, Cleavage vs. Fracture, Hardness, & Specific Gravity
The characteristics of a mineral can help you identify a mineral. For example:
1. Color - the least important property of a mineral, since chemical impurities can change the
color of the same mineral
2. Luster - The property that describes the way a mineral shines in light.
 Described as Metallic (looks like a metal) or Nonmetallic
3. Streak - The property of a mineral that describes its color in powdered form
 When a mineral is rubbed across an unglazed tile of white porcelain (a streak plate), it
leaves a line of powder.
 The color of the streak is always the same. For example, quartz leaves a white streak,
whether it's violet (amethyst), pink (rose quartz), or brown (smoky quartz).
4. Cleavage - The tendency of a mineral to split along flat surfaces where bonds are weakest.
Some minerals break only in one direction; others break in two or more directions.
 Cubic: form cubes
 Rhombohedral: form six-sided prisms
 Basal: occur along a single plane parallel to the base (flat layers)
5. Fracture - The property of a mineral that describes an irregular pattern of breakage in a
direction other than along cleavage planes.
The mineral splits in no particular direction when broken.
 Conchoidal Fracture: smooth, curved fracture like the inside of a clam shell
 Fibrous/Splintery Fracture: looks like splinters
6. Hardness - The resistance of a mineral to scratching
Moh’s Scale of Hardness:
7. Specific Gravity - The ratio of the weight of a substance to the weight of an equal volume of
water.
8. Other Properties - Any other special property of a mineral that distinguishes it from others.
•
Double Refraction: when a mineral splits the light rays that pass through it, making a
single object appear as two objects when you look through the mineral (example calcite)
•
Magnetic: affects a compass (example magnetite)
•
Fluorescent: when a mineral glows under an ultraviolet light (example fluorite)
•
Salty taste: when a mineral tastes like salt (example halite.) DO NOT TEST YOUR
MINERALS FOR THIS!!!
•
Radioactive: when a mineral gives off subatomic particles that are detected by a Geiger
counter (example uraninite.)
•
Chemical Tests: when hydrochloric acid is dropped on the mineral Calcite, it will fizz or
“Effervesce.”The released bubbles are carbon dioxide gas.
•
Some minerals can be identified by SMELL for example Sulfur can smell like rotten eggs
or a burnt match.