Gems+and+Minerals

=**Gems and Minerals**=

Mineral
From the [|International Mineralogical Association]) - A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes.

From the [|Miriam-Webster Dictionary] - A solid homogeneous crystalline chemical element or compound that results from the inorganic processes of nature ; //broadly// **:** any of various naturally occurring homogeneous substances (as stone, coal, salt, sulfur, sand, petroleum, water, or natural gas) obtained usually from the ground b **:** a synthetic substance having the chemical composition and crystalline form and properties of a naturally occurring mineral

Gemstone
From the [|Miriam-Webster Dictionary] **-** **A** mineral or petrified material that when cut and polished can be used in jewelry

Color of Gemstones
__Cause.__ The color of gemstomes is caused by a trace impurities trapped within the crystalline structure. These impurities are usually transition metals with partially filled 3d electron orbitals. An energy change occurs when these electrons absorb visible light which is then emitted when the electrons return to their ground states. Sometimes color can be produced by nuclear decay. In the case of yellow diamonds, a carbon-14 atom undergoes ß-decay to form a nitrogen atom that is part of the 3-D structure of the diamond. Because nitrogen and carbon have different valences, carbon can receive an electron from nitrogen in an intervalence transition causing a yellow color. Similarly, a blue diamond is caused by trace amounts of boron. Both yellow and blue diamonds can act as semiconductors. Nitrogen can donate an electron to carbon while boron accepts an electron from carbon. Thus, yellow diamonds act at donors and blue diamonds as acceptors. About 1 in 100,000 carbon atoms is replaced by a nitrogen atom in a yellow diamond. In blue diamonds, the substitution is approximately 1 in 1,000,000. When plastic deformations occur during crystal growth, the resulting diamonds may be pink or brown.

__The conundrum of corundum.__ Rubies and sapphires are mostly composed of aluminum oxide, also known as corundum. The only chemical difference between these gems is the elemental impurity. In rubies, trace amounts of chromium(III) ions replace about 1% of the aluminum ions. This substitution sets up an energy difference in the orbitals of chromium ions. When white light strikes a ruby, some is absorbed causing a transition in energy of elections and emission of light. In sapphires, pairs of aluminum ions are replaced by iron(II) and titanium(IV) ions. When energy is absorbed, electron transfer between the iron and titanium ions occurs in an “intervalence transition.”

Gemstones and Chemical Formulas
Al3+ in adjacent octahedral sites || || Al3+ in adjacent octahedral sites || || blue or yellow || Color centers from nitrogen atoms trapped in crystal || ||
 * **Gem** ||< **Formula** ||= **Color** || **Origin of Color** ||  ||
 * Ruby ||< Al 2 O3 ||= Red || <span style="font-family: Arial, Helvetica, sans-serif;">Cr3+ replacing Al3+ in octahedral sites || <span style="font-family: Arial, Helvetica, sans-serif;">[[image:ruby.jpg width="51" height="56"]] ||
 * <span style="font-size: 10pt; font-family: Arial, Helvetica, sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA; msofareastfontfamily: 'Times New Roman'; msoansilanguage: EN-US; msofareastlanguage: EN-US; msobidilanguage: AR-SA;">Emerald ||< <span style="font-size: 10pt; font-family: Arial, Helvetica, sans-serif; msofareastfontfamily: 'Times New Roman'; msoansilanguage: EN-US; msofareastlanguage: EN-US; msobidilanguage: AR-SA;">Be3Al2(SiO3)6 ||= <span style="font-family: Arial, Helvetica, sans-serif;">Green || <span style="font-size: 10pt; font-family: Arial, Helvetica, sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA; msofareastfontfamily: 'Times New Roman'; msoansilanguage: EN-US; msofareastlanguage: EN-US; msobidilanguage: AR-SA;">Cr3+ replacing Al3+ in octahedral site || <span style="font-family: Arial, Helvetica, sans-serif;">[[image:EMERALD045Y.jpg width="64" height="49"]] ||
 * <span style="font-family: Arial, Helvetica, sans-serif;">Garnet ||< <span style="font-size: 10pt; font-family: Arial, Helvetica, sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA; msofareastfontfamily: 'Times New Roman'; msoansilanguage: EN-US; msofareastlanguage: EN-US; msobidilanguage: AR-SA;">Mg3Al2(SiO4)3 ||= <span style="font-family: Arial, Helvetica, sans-serif;">Red || <span style="font-size: 10pt; font-family: Arial, Helvetica, sans-serif; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA; msofareastfontfamily: 'Times New Roman'; msoansilanguage: EN-US; msofareastlanguage: EN-US; msobidilanguage: AR-SA;">Fe2+ replacing Mg2+ in 8-coordinate site || [[image:Garnet-web.jpg width="81" height="77"]] ||
 * Peridot ||< <span style="font-size: 10pt; font-family: Arial; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">Mg2SiO4 ||= Yellow-green || <span style="font-size: 10pt; font-family: Arial; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">Fe2+ replacing Mg2+ in 6-coordinate site || [[image:peridot.jpg width="70" height="70"]] ||
 * <span style="font-size: 10pt; font-family: Arial; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">Sapphire ||< <span style="font-size: 10pt; font-family: Arial; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">Al2O3 ||= Blue || <span style="font-size: 10pt; font-family: Arial; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">Intervalence transition between Fe2+ and Ti4+ replacing
 * <span style="font-size: 10pt; font-family: Arial; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">Aquamarine ||< <span style="font-size: 10pt; font-family: Arial; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">Be3Al2(SiO3)6 ||= Blue || <span style="font-size: 10pt; font-family: Arial; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">Intervalence transition between Fe2+ and Fe3+ replacing
 * <span style="font-size: 10pt; font-family: Arial; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">Diamond ||< C ||= Colorless, pale

Classification by Crystal Structure
(more information can be found here [])
 * ===description=== ||< ===examples=== ||
 * Cubic ||< diamond, garnet ||
 * Tetragonal ||< zircon ||
 * Hexagonal ||< aquamarine, beryl, emerald ||
 * Trigonal ||< amethyst, citrine, ruby, sapphire, quartz ||
 * Orthorhombic ||< chrysoberyl, peridot, topaz ||
 * Monoclinic ||< azurite, feldspar ||
 * Triclinic ||< turquoise ||
 * Amorphous ||< amber, ivory, opal, pearl ||

Classification by Chemical Composition
Vanadates, Tungstenates, Molybdates || (AO4)2- where A = P, Sb, As, V || turquiose || Ex: (SIO4)4-, (Si2O7)6-, etc || beryl, garnet, amethyst, citrine, onyx, quartz || (more information on the [|Dana Classification System])
 * ===Group Number=== ||= ===Type=== || ===Chemical Abbreviations=== || ===Example=== ||
 * = 1 || Native Elements || Au, Ag, C, Pt || gold, silver, diamond, platinum ||
 * = 2 || Sulfides || S2- || pyrite ||
 * = 3 || Oxides, Hydroxides || O2-, OH- || corundum (ruby, sapphire) ||
 * = 4 || Halides || F-, Cl- || flourite ||
 * = 5 || Carbonates, Nitrates, Borates || (CO3)2-, (NO3)-, (BO3)3- || azurite, calcite, malachite ||
 * = 6 || Sulfates, Chromates || (SO4)2-, (CrO4)2- || gypsum ||
 * = 7 || Phosphates, Arsenates
 * = 8 || Silicates || Si and O2 combinations
 * = 9 || Organic || oxylates, hydrocarbons, etc || amber, obsidian, opal, pearl ||

A comprehensive list of minerals sorted by element can be found [|here]. .

Hardness of Gems and Minerals
The Mohs Scale of Hardness is used to compare the resistance to scratching of different substances. This is not a linear scale but is useful nonetheless. The values for various substances is shown in the table below.

Table from [|American Federation of Mineralogical Societies].
 * <span style="font-family: arial, Arial, Helvetica;">** Hardness ** || <span style="font-family: arial, Arial, Helvetica;">** Mineral ** || <span style="font-family: arial, Arial, Helvetica;">** Associations and Uses ** ||
 * <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">1 || <span style="font-family: arial, Arial, Helvetica;">Talc || <span style="font-family: arial, Arial, Helvetica;">Talcum powder. ||
 * <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">2 || <span style="font-family: arial, Arial, Helvetica;">Gypsum || <span style="font-family: arial, Arial, Helvetica;">Plaster of paris. Gypsum is formed when seawater evaporates from the Earth’s surface. ||
 * <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">3 || <span style="font-family: arial, Arial, Helvetica;">Calcite || <span style="font-family: arial, Arial, Helvetica;">Limestone and most shells contain calcite. ||
 * <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">4 || <span style="font-family: arial, Arial, Helvetica;">Fluorite || <span style="font-family: arial, Arial, Helvetica;">Fluorine in fluorite prevents tooth decay. ||
 * <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">5 || <span style="font-family: arial, Arial, Helvetica;">Apatite || <span style="font-family: arial, Arial, Helvetica;">When you are hungry you have a big "appetite". ||
 * <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">6 || <span style="font-family: arial, Arial, Helvetica;">Orthoclase || <span style="font-family: arial, Arial, Helvetica;">Orthoclase is a feldspar, and in German, "feld" means "field". ||
 * <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">7 || <span style="font-family: arial, Arial, Helvetica;">Quartz ||  ||
 * <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">8 || <span style="font-family: arial, Arial, Helvetica;">Topaz || <span style="font-family: arial, Arial, Helvetica;">The November birthstone. Emerald and aquamarine are varieties of beryl with a hardness of 8. ||
 * <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">9 || <span style="font-family: arial, Arial, Helvetica;">Corundum || <span style="font-family: arial, Arial, Helvetica;">Sapphire and ruby are varieties of corundum. Twice as hard as topaz. ||
 * <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">10 || <span style="font-family: arial, Arial, Helvetica;">Diamond || <span style="font-family: arial, Arial, Helvetica;">Used in jewelry and cutting tools. Four times as hard as corundum. ||

Hardness of other items;


 * = **Hardness** || **Item** ||
 * = <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">2.5 || <span style="font-family: arial, Arial, Helvetica;"> Fingernail ||
 * = <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">2.5–3 || <span style="font-family: arial, Arial, Helvetica;">Gold, Silver ||
 * = <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">3 || <span style="font-family: arial, Arial, Helvetica;">Copper penny ||
 * = <span style="display: block; font-family: arial, Arial, Helvetica; text-align: center;">4-4.5 || <span style="font-family: arial, Arial, Helvetica;">Platinum ||
 * = <span style="font-family: arial, Arial, Helvetica;">4-5 || <span style="font-family: arial, Arial, Helvetica;">Iron ||
 * = <span style="font-family: arial, Arial, Helvetica;">5.5 || <span style="font-family: arial, Arial, Helvetica;">Knife blade ||
 * = <span style="font-family: arial, Arial, Helvetica;">6-7 || <span style="font-family: arial, Arial, Helvetica;">Glass ||
 * = <span style="font-family: arial, Arial, Helvetica;">6.5 || <span style="font-family: arial, Arial, Helvetica;">Iron pyrite ||
 * = <span style="font-family: arial, Arial, Helvetica;">7+ || <span style="font-family: arial, Arial, Helvetica;">Hardened steel file ||

Resources for gemstones:
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