lesson 23/24: rocks and minerals Flashcards
minerals
- They are a naturally occurring solid substance that is found in the Earth’s crust.
- They have a definite crystalline structure.
- most minerals contain two or more elements, but some can be found in their pure form.
- There are two types of minerals, metallic and non-metallic.
- They are very important in our daily lives.
ore
- Also called metallic minerals
- They are extracted by mining.
- They are valuable metals that are extracted from them.
- An example of this is bauxite, copper pyrite, and hematite.
rock
- These are non-metallic minerals.
- Some examples of this are talc, stones, gems, and gypsum.
- Rocks are made up of minerals.
properties of a mineral
- Minerals must be naturally occurring substance.
- Minerals have to be solid.
- They cannot have a definite chemical composition.
- They must have a crystal structure.
- And minerals must be inorganic (cannot be derived from a living substance)
class
This guide uses the most common classification system for minerals, created by a German mineralogist. It divides mineral specimens into nine classes expressed by a roman numeral and name.
I. Elements
II. Sulphides
III. Halides
IV. Oxides and hydroxides
V. Carbonates, nitrates, and borates
VI. Sulphates, chromates, molybdates, wolframates
VII. Phosphates, arsenates, vanadates
VIII. Silicates
IX. Organic minerals
crystal system
Crystalline solids have their particles (atoms, ions, and molecules) arranged in a particular way. The basic structure is the unit cell. A crystal is formed by repeating this cell. There are 7 crystal systems, each defined by the relative length of the side of the unit cell (a, b, c) on the unit cells internal angles. Solid minerals in which the particles have no particular arrangement are described as ‘amorphous.’
crystal
Most minerals produced crystals with more than one external form, but, on the whole, species have a typical form that is most commonly seen. This form is given in the summary table.
hardness
The hardness of a mineral is classified by its ability to resist scratching an abrasion. Hardnesses equality that is highly prized, especially in gemstones, since it relates directly to durability. The Mohs scale measures this property in a practical way: each mineral on the scale can scratch the one that precedes it but is scratched by the one that follows it. However, the hardness of a mineral can vary depending on the direction in which it is scratched. For this reason, some minerals are given two Mohs scale numbers, indicating their minimum and maximum hardness.
1. Talc (weakest mineral)
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Orthoclase
7. Quartz
8. Topaz
9. Corundum
10. Diamond (hardest mineral)
fracture and cleavage
is the tendency of a crystal to split along certain regular planes, leaving newly exposed faces that are flat and smooth. Crystals that split irregularly a said to fracture. Fractures may be fibrous or splintery, conchoidal (shell shaped), or scaly.
lustre
Is a way of describing how light interacts with the surface of a gemstone or mineral. Many different terms are used, for example, muscovite is said to have pearly lustre and chalcedony wax lustre. Looking minerals with no real lustre or shine are described as dull. Two of the most common types of lustre are metallic and submetallic. Minerals with them italic last to include pyrite as they shine like metals do. Minerals with a submetallic lustre are those that are normally opaque but come transparent if they’re cut into thin sheets.
streak
is the colour of a mineral that is left when it is dragged across a rough, white, surface, usually unpolished porcelain. The mark is made up of a tiny, powdery fragments of the mineral. “Streak colour; is sometimes used to describe this, as well as the more common simple ‘streak’. Streak is normally used for minerals with a hardness of less than 7, as this is the hardness of porcelain.
