Minerals and rocks | Buy minerals

Minerals and rocks

Identifying rocks and minerals is not an easy job..To be able to identify rocks and minerals you must first know the basics.

Identifying rocks and minerals

A rock is a mixture or an accumulation of different minerals,For example,Granite is a rock while it can have the minerals Quartz,Feldspar,Mica and so on.

Rocks are divided into mainly 3 categories:

•Igneous:It is when magma or lava cools and crystallizes.They are divided into two groups:

1.Intrusive:It is when the magma cools slowly under the earth and forms large crystals.
2.Extrusive:It is when the lava cools rapidly on the surface of the earth and forms small or no crystals.

•Sedimentary:It is when sand and other minerals or even organic matter deposits and compacts together to form a rock.

•Metamorphic:It is when other rocks even past metamorphic rocks melt and under pressure and heat recrystallizes and form another mineral.

The definition of a mineral is:

•A naturally occurring solid chemical substance that is created through geological processes and has distinct physical properties,extremely arranged atomic structure, and a unique chemical composition.

A mineral can be classified through mainly 7 ways which are:

•Hardness:It is how hard the mineral is physically and what can it be scratched by on the Moh hardness scale from 1 to 10,for example Fluorite,CaF₂ has a hardness of 4 so it can be scratched by a knife blade.
1.Talc Mg₃Si₄O₁₀(OH)₂ (Scratched by fingernail)
2.Gypsum CaSO₄·2H₂O (Scratched by fingernail)
3.Calcite CaCO₃ (Scratched by copper penny)
4. Fluorite CaF₂ (Scratched by knife blade)
5.Apatite Ca₅(PO₄)₃(OH,Cl,F) (Scratched by knife blade)
6.Orthoclase KAlSi₃O₈ (Scratched by steel file)
7.Quartz SiO₂ (Scratched by hardened steel)
8.Topaz Al₂SiO₄(OH,F)₂ (Scratches anything lower)
9.Corundum Al₂O₃ (Scratches anything lower)
10.Diamond C (Scratches everything else)

•Streak:It's the color of the powder when the mineral is rubbed on an unglazed porcelain plate,It's not always the same as the minerals color,For example quartz can be many colors such as brown,violet,gray,yellow etc. But it's streak color will always be white.

•Luster:To put it simply,It's how a mineral reflects light.They are divided into 3 groups:
1.Metallic:Reflects light very well just like a polished metal.

2.Sub-Metallic:Reflects light like a dull or weathered metal.

3.Non-metallic:Divided into other sub-categories which are:
A.Adamantine:Having the reflection of a diamond.
B.Glassy:Having the reflection of glass.
C.Resinous:Not very glassy,like Sphalerite or Amber.
D.Greasy:As if it was coated with oil.
E.Pearly:Having the look or reflection of a pearl.
F.Silky:Looks like silk,Has fiber or thread like structure on its surface.
G.Dull:Having little or no reflection.
H.Earthy:Like clay or soil.

•Color:It is not a very reliable way of identifying minerals unless you're an expert and already know the colors of many minerals,Since the color of the mineral can change even with a slight impurity.For example Quartz, it's true color is white or clear,but it can have other colors such as rose quartz(Pink),due to impurities.

•Specific gravity or density:It's how heavy the mineral is per given volume,D=M/V. An easier way to find the specific gravity or density is by carrying the mineral in your hand and then feeling if it is too heavy for it's size,too light,or perfect for it's size.

•Cleavage And Fracture:Cleavage is the tendency of a mineral to break into crystal pieces or smooth planes,If it doesn't then the mineral has no cleavage.
Cleavages can be:

1.Perfect
2.Good
3.Poor
4.None.

Perfect cleavage means that the mineral is very smooth.
Good cleavage means its smooth but has some jagged or rough surfaces.
Poor means it is very hard to notice the smoothness and is jagged and rough.
None means the mineral is not smooth and is entirely jagged or rough.

Cleavages can be in 4 directions:

1.One direction
2.Two directions
3.Three directions
4.All directions(4 or more directions)

Some of the patterns of cleavage in minerals are:

1.Cubic:3 Cleavages 6 faces at right angles,Small cubes break off actual cube.
2.Prismatic:2 Cleavages 4 faces of several probable angles third side fractures irregularly,Small vertical prism like shapes break off.
3.Basal:1 Cleavage 2 faces,Small flat like pieces break off.
4.Rhombohedral:3 Cleavages 6 faces not at right angles,Small rhombus like pieces break off.
5.Octahedral:4 Cleavages 8 faces,Flat triangular pieces break off.

Fracture:A fracture is the definite mark left on the mineral after it was broken or chipped off.
Some types of fractures are:

1.Uneven:Irregular or rough surface.
2.Smooth:Smooth surface.
3.Crumbly:Crumbles when broken.
4.Jagged:Irregular sharp edges.
5.Conchoidal:Smooth curved surface like the inside of a shell.
6.Fibrous:Fibers or Splinters.
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•Mineral Habit:It's the common appearance that the mineral crystal usually has:
Some mineral habits are:

1.Tabular:It looks like a little amount of paper put together (thin) or a large amount of paper put together (thick).
2.Acicular:Looks like needles.
3.Equant:Sphere or cube like.
4.Prismatic:Prism like.
5.Capillary:Hair like.
6.Bladed:Like thin flat blades.
7.Divergent:Fan like or like rays going outward.
8.Dendritic:Cluster of fern like leaves.
9.Druzy:crystals on the surface of a mineral.
10.Reticulated:Interconnected lattices.
11.Fibrous:Fiber like.
12.Globular:Packed spheres going outward.
13.Columnar:Big column like cluster.
14.Stellate:Thin crystals going outward in all directions.
15.Mamillary:Bowl or Human breast like.
16.Botryoidal:Like a bunch of grapes.
17.Reniform:Packed clusters together going outward.
18.Plumose:Like dendritic but much finer.
19.Foilated:Like overlapping leaves.
20.Micaceous:Like overlapping leaves but breaks into thin sheets.
21.Lamellar:Like flat thick overlapping leaves.
22.Banded:Different bonding of layer of colors.
23.Massive:No crystal structure.
24.Concentric:Semi circular like patterns from the center to the edge.
25.Pisolitic:Small round masses.
26.Oolitic:Very small round sphere masses.
27.Geode:A rock with a hollow inside it that is in the shape of mineral crystals.

Some other mineral properties are:
•Magnetism:If the mineral displays magnetic properties.
•Acid test:If the mineral reacts with dilute acid.
•Taste:Some evaporite minerals have distinct tastes.