Silicate Minerals: Formulas and Structures

• Chapter focuses on matter and minerals, aiming to teach the reader about mineral definitions, polymorphs, solid solutions, crystal growth, mineral characteristics, silicate structures, mineral classifications, and non-silicate groups

Mineral Definition

• A mineral is a naturally formed solid, possessing an ordered 3D internal arrangement of atoms and a specific chemical composition
• Water is not a mineral because it is a liquid, not a solid
• Ice is a mineral if it forms naturally like a snowflake
• Ice is not a mineral if humans play a role in its production
• Mineral names are unsystematic and can originate from place names, personal names, mine terms, or mystical origins

Elements

• An element is a substance unalterable into simpler substances through chemical or physical means
• The fundamental unit of an element is the atom
• An atom includes protons, neutrons, and electrons
• A proton is a dense particle with a positive charge
• A neutron possesses similar mass to a proton but lacks electrical charge
• An electron is a very dense particle with a negative charge
• Electrons are believed to move within regions around the nucleus, called energy levels
• Energy levels can hold a specific amount of electrons, with the outermost level containing valence electrons
• The atomic number, defined by the number of protons in the nucleus, dictates the chemical properties of each atom
• Elements are cataloged by atomic number
• Uranium, with 92 protons in its nucleus, has the highest atomic number of naturally occurring elements
• Around 1864, chemists classified elements by increasing weight, resulting in Mendeleev publishing the periodic table
• Atomic weight equals the sum of protons and neutrons in an atom's nucleus
• The atomic mass of an element is determined relative to another atom
• Carbon-12 is set at 12 amu (atomic mass units) as the current standard
• Isotopes are atoms sharing atomic numbers but differing in atomic weights
• Carbon-12, carbon-13, and carbon-14 contain six protons but unique mass numbers
• Atomic bonding describes chemical and physical stability
• Specifically when valence electron shells are filled consisting of eight electrons.
• Atoms lacking four or fewer valence electrons tend to donate electrons
• While electrons can be donated, atoms possessing more than four valence electrons will accept electrons
• The number of protons and electrons are not equal, this results in charge, positive or negative
• Ions are atoms that do not have equal quantities of protons and electrons
• An atom that loses a proton will have a positive charge and is called Katioon
• An atom that gains an electron will have a negative charge and is called Anioon
• A molecule refers to the smallest unit retaining distinct chemical properties of a compound
• molecular compound comprises two or more atoms held together
• The force maintaining the compilation is called bonding
• Connective force dictates chemical and physical characteristics within compound

Types of Bonding

• Electron transfers between atoms producing cations and anions are called ionic bonds
• Covalent bonding occurs when one or more pairs of electrons are shared by two atoms
• Van der Waals bonding occurs due to secondary attraction between molecules formed by transferring electrons
• Metallic bonding occurs when atoms share electrons in higher energy-level shells, freeing valence electrons to migrate between atoms

Mineral Structure

• Both crystals and crystalline solids are any natural solid with ordered, repetitive, atomic structure
• A crystal will grow on a continuous piece consisting of plane outer surfaces referred to as crystal faces
• Crystals form best in free space and are deemed rare or are prized samples
• One mineral will be comprised of same crystal faces and corresponding face meet at diagnostic angle
• New mineral crystals are usually created in five methods
• Solidification of a melt will crystallize liquid into solid
• Water molecules of ions dissolved in compounds bond out of central of water
• The slow movement of atoms or ions through a solid
• The interface of bodies producing minerals on themselves or around those said bodies
• Gases that precipitate around volcanic vents and/or geisers
• Minerals consist of array of chemically bound atoms creating crystalline structure

Ion Size

• Internal atomic arrangement in compounds stems from ion size
• Anions combine to counteract the effects of charges
• Atomic packing will define structural structure of mineral
• The orderly arrangement controls shape or morphology of crystals
• Crystal structures that are packed tightly or differently can yield a variety of crystal structures

Solid Solution Series

• Solid solution happens when elemental structure is switched out for atoms that share similar chemical and physical properties
• Solid series is categorized in several ways and some of the main types are as follow
• Olivine that makes Mg2SiO4 forsterite and Fe2SiO4 fayalite is known as a solid solution
• Amorf that includes atomic structures not well defined like glass
• Glass equivalent to crystal quartz is known as crystalline

Identifying Minerals

• Identifying minerals can be done by color and while some have definitive color some have variable color based on the mineral itself
• Another way is by streak which can be very important for diagnostic purposes; this process involves the mineral being scraped to see whether it has color streaking
• External color and streaking is never the same
• Minerals can be determined by glancing at the light and whether it is metallic or nonmetallic
• Hardness is also determining or measuring how resistant scraping may be
• Friedrich Mohs made method for creating a tiered scale for comparing atomic stability
• Next attribute that aides in identification is measuring whether the mineral is apt to breaking in certain patterns, which happens along planar surfaces
• Cleavage surface is breakage of certain surface on a crystal Plainer directions indicate bonds between atoms are weak
• Non-existent planes exist due to tightly bonded atoms, which break with distinct fractures
• Other terminology around break will have certain appearances of forms
  • Fibrous, Asbestos
• Irregular shape with broken edge
• Hackly as found in native metals
• Density or S.G describes minerals volume to weight when measured and can denote heaviness
• The formula can be understood as a mineral's density divided by Water's
• All minerals have direction as described or exhibited
• Crystal forms are a way of referring characteristics to mineral such as:
  • Habit of needle or cubic structure
  • Can be found by reacting certain gas with diluted material

Classifying Minerals

• There are about 4000 identified minerals while on 30 have been actively encountered
• Typically they be will categorized through dominating Anion
• The mineral classes that are often encountered have
  • Dominant amounts Silicates
  • Cl,F, Br and/or I (Halides)
  • Oxygenated (Oxides)
• Hydroxide materials
• Carbons
• Sulphates
• Phosphates
• Pure elements
• Sulphur

Silicate Materials

• Dominant group of element
• Contains greatest amount rock-forming minerals
• Highly abundant
  • Silicon Si
  • Oxygen O
• Key structural element is silicon-oxygen tetrahedron molecules
  • Basic construction is (SIO)4)4) that's joined by Cations
• Two groups in crystal structre: ferromagnesium and non
  • Contain lesser amount Fe and/or Mg
  • Contain substantial Fe and/or Mg Tetrahedral of 7 groups

Nesosilicates

• Linked by Cations such as Olivine
  • Constructed of Magnesium and or Iron linked by Silica Dioxide
  • One with high densities
  • Sirkoon (ZrSIO4) Tetrahedral structures
• Garnet
• (X3Z2(SIO4)3)
  • Chemise composition dictated by elements of group such:
  • Pyrope
  • Almadine
  • Spessartine

Sorosilicates or Double Tetrahedrons consisting of (SI2O7)-6

• Constructed from two Tetrahedrons bonded
  • Most are hard and planar by properties
  • These are very common and come the form of Epidote
• Others are also
• Zoisite are made with SI4) and/or O76 Ions
• Clinozoisite that has Carbon bonds
• Tansaniet has strong Carbon bonds
• Allaniet makes Carbon bond by using two elements
• Fe2 and Fe3

Ring Silicates

• Link in circle shape within Tetrahedron structures
  • Each Carbon bonded to O2 with another with tetrahedral bond
• • Each ring is built with three or four bonds
  • Can be made with good shine and be very difficult to break
  • Most types
• Beryl B3AI2(SIO3)6 -
• Tormalyn (Na, CA)(AI, Li Mg)(AI, Fe, Mn)6(SI6O18), Bo3, (OH)4

Enkel Ketting or Inosilikates with (SiO3) ^ 2

• Make 2-0 tetrahedron bond forming chains
• Forms groups such as Pryoxene XY(SI, AL)06
• Most common are such Enstatite Mg,SI,O6 Augiet- CaMg(SIAI)206-
• All has rigth angle with splyting

Dubbelketting Silikate known as Inosilakates with (SI ^ 04, 11-6 or SIO8.22.12

• Have to have certain amount Carbon next to each other because has 26 oxygen bonds Amphibol group is main class and consist of
• Prismatic needle or fibre shape features
• Right angle of splyting

Plaat Silikates

• These make rings and attach to make plates and are joined to make crystal structures

  • Some kinds:
  • Mica that also hydrates
  • Makes some other structures

• Talk Mg6 (SI8020), OH4 -Chloriet (MgFEMN) (SIAL),O23 Asbestos: hydrated serpentines Most can be non cancerous with

• Clay Materials

Raamwerk Silikates( Tektonsilikates)

• Connected to make outside structure to make large framing area for other minerals to form
• Consist of two things
  • Veldspaar (A, L, Si,08)
• Ziolites which hold water in structural make up
• Made with Al
• Highly resistant

Test your knowledge of silicate minerals. Questions cover chemical formulas like Pyrope and Almandine. Also test your understanding of silicate structures and diagnostic properties.