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 SiliconOxygen.
•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.
4. Definite Chemical Composition
•Minerals always have the same chemical makeup.
•Ex: The formula for Quartz will always consist of one-part Si and two parts O.
•Rocks on the other hand can be made of different combinations of minerals or mineraloids.
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
Tetragonal
3 axes of symmetry: 2 same length, one different
All 90 ° angles
Zircon
Hexagonal
4 axes of symmetry
3 same length at 120° angle
1 different length at 90° angle
Quartz
Orthorhombic
3 unequal axes of symmetry
All 90° angles
Topaz
Monoclinic
3 unequal axes of symmetry
Two at 90° angles, one not
Gypsum / Calcite
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 heatpressure.
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 (can be glassy, pearly, waxy, dull or earthy.)
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 –breaks in 3 directions along 3 cleavage planes. Ex: Halite
Rhombohedral: form six-sided prisms when broken. Ex: Calcite
Basal: occur along a single plane parallel to the base (peels off in flat layers)Ex: Mica
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. Tells you how many times denser the mineral is than 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.