What is a mineral

1
What is a mineral

• Four requirements to be a mineral
• 1- Naturally occurring
• 2- Inorganic solid
• 3- Specific chemical composition
• 4- Definite crystalline structure
• __________________________________
• Each mineral has unique characteristics,
• About 3000 minerals on Earth, but only about 10
  make 90 of the rocks in Earths crust (0.003
  of total of minerals)

2
Mineral characteristics

• 1- Naturally occurring- No synthetic or
  manufactured material fits this condition
• 2- Inorganic solid- No material (even naturally
  occurring) that is made by biotic means.
• 3- Solid w/ specific composition- Most often a
  combination of elements (compounds), but a few
  are single elements. Minerals may have the same
  elements, but their proportion and arrangement
  are unique.
• 4- Definite crystalline structure- A repeated
  pattern of crystal arrangement (one of 6 crystal
  systems)

3
What is not a mineral -Mineraloids and Rocks

• Mineraloids - Some materials, even naturally
  occurring fit the conditions, except for the
  orderly internal (crystalline) structure (Ex.
  Opal)
• Rocks Any solid mass of mineral, or
  mineral-like matter that occurs naturally as part
  of our planet. Some types
• - Composed almost entirely of one mineral (ex.
  Limestone)
• - Aggregates of several minerals (most rocks,
  ex. Granite, which is a combination of quartz,
  feldspar, hornblende)
• - Composed of non-mineral matter
• non-crystalline, glassy volcanic rocks
  (obsidian, pumice) solid organic debris (coal)

4
Crystals and Crystal Systems

• Definition of Crystal - Regular polyhedral form,
  bounded by smooth faces, assumed by a chemical
  compound, due to the action of its inter-atomic
  forces, when passing, under suitable conditions,
  from liquid or gas to a solid.
• 1- Polyhedral solid bounded by flat planes
  (Crystal Faces)
• 2- Change from liquid or gas to solid Liquids
  and gases dont have definite shape (take shape
  of container), solids take on one of several
  regular geometric forms. These forms may be
  subdivided, using geometry, into six systems
• 1- Cubic
• 2- Tetragonal
• 3- Hexagonal
• 4- Orthorhombic
• 5- Monoclinic
• 6- Triclinic

5
Basis for Crystal Systems

• Some geometry
• CRYSTALLOGRAPHIC AXES.
• - We have 3 dimensions, so we must have 3 axes.
• - For a moment, let's make them all equal and at
  right angles to each other. This is the simplest
  case. The axes pass through the center of the
  crystal and, by using them, we can describe the
  intersection of any given face with these 3 axes.
  

6
Basis for Crystal Systems

• Axes
• Number Length angles
• ____________________________
• 1- Cubic 3 equal 90
• 2- Tetragonal 3 2 equal 90
• 3- Hexagonal 4 3 equal variable
• 4- Orthorhombic 3 all diff. 90
• 5- Monoclinic 3 all diff. variable
• 6- Triclinic 3 unequal all different

7
But not all crystals are ideal !!(Most are not.)

• Your mineral crystal that does not match the
  pictures books.
• You may have is a distorted crystal form where
  some faces may be subordinate or missing.
  Distorted crystals are common and result from
  less-than-ideal growth conditions or even
  breakage and recrystallization of the mineral.
  However, remember that we must also be comparing
  the angles between similar faces. If the faces
  are not present, then you cannot compare them.
  With many crystals we are dealing with a final
  shape determined by forces other than those of
  the interatomic bonding.
• During the process of crystallization in the
  proper environment, crystals assume various
  geometric shapes dependent on the ordering of
  their atomic structure and the physical and
  chemical conditions under which they grow. If
  there is a predominant direction or plane in
  which the mineral forms, different habits
  prevail. Thus, galena often forms equate shapes
  (cubes or octahedrons), quartz typically is
  prismatic, and barite tabular.

8
Mineral and Crystal formation

• From Magma (molten matter from beneath Earths
  surface)
• - Elements and proportion in magna Type of
  minerals formed
• - Rate of cooling Size of crystals formed
  (slow-large crystals, fast-small)
• From solutions.
• - By precipitation In saturated solutions,
  mineral crystals precipitate.
• - By evaporation Only water leaves, minerals
  stay behind

9
Common Mineral and Elements

• Of the 4000 minerals on Earth, about 30 are
  common Rock forming minerals.
• About 90 elements occur naturally on Earths
  crust. The great majority of minerals are made of
  8 common elements
• Oxygen Aluminum Calcium Potassium
• Silicon Iron Sodium Magnesium
• All other elements combined make 1.7
• Oxygen (46.6) and Silicon (27.7) are the most
  common.
• In contrast, 6 elements are most common within
  living organisms (Carbon, Oxygen, Nitrogen,
  Hydrogen, Phosphorous and Sulfur).

10
Mineral Groups

• 1- Silicates
• 2- Carbonates
• 3- Oxides and hydroxides
• 4- Halides
• 5- Sulfates
• 6- Sulfides
• 7- Native elements

11
SILICATES

• - 96 of minerals in Earths crust
• - Contain O, Si and 1 or more elements.
• - Form Silica tetrahedron molecules, each made
  of 1 Si atom attached to 4 Oxygen atoms. This
  arrangement allows sharing Oxygen atoms among
  tetrahedron molecules and determines the great
  variety of silicates.
• - Various arrangements of tetrahedron molecules
  are common Single chain, double, Sheet.
• - The bonds between the other atoms in the
  silicate determine properties, particularly how
  they split.
• - Examples Quartz, feldspar, olivine, topaz,
  Mica

12
Carbonates and Oxides

• Carbonates
• - One or more metallic elements, with a
  carbonate group (CO3).
• - Examples Limestone (used commercially for
  road paving, building stone and cement), Marble
  (used decoratively)
• Oxides
• - Oxygen and a metal.
• - Examples Hematite and Magnetite (Ore of Iron
  source of iron), Uraninite (source of uranium)

13
Sulfides, Sulfates, Halides Native Elements

• Sulfides
• - Sulfur and one more element (pyrite FeS2)
• Sulfates
• - Include the sulfate compound SO4 (anhydrate
  Ca SO4)
• Halides
• - Chloride or Fluoride, along with Ca, Na or K
  (Salt NaCl)
• Native elements
• - Silver (Ag), Copper (Cu) occur naturally alone.