Minerals: Halides

Minerals are defined by five criteria: 1. Naturally Occurring, 2. Inorganic, 3. Solid, 4. Defined Chemical (Atomic) Formula, and 5. A unique set of physical properties.

Halides

-are compounds in which metallic elements combine with halogens (the elements chlorine, bromine, fluorine and iodine). Halides are common in a number of geological environments. Some, such as halite, are found in the evaporite seqience.

Specimen: Halite
Name origin: From the Greek άλς, sea, for halites, later modified by J.D. Dana to halite.
Classification: Halides
Chemical Composition: NaCl
Color: Colorless, whitish, yellow, red, purple, or blue
Crystal structure: Isometric (Cubic)
Hardness: 2.5 Mohs scle
Specific Gravity: 2.168
Luster: Vitreous
Diaphaneity: Transparent to translucent
Streak: White
Cleavage: Perfect cube
Tenacity: Brittle
Fracture: Conchoidal
Source: Natural sodium chloride (also named rocksalt; water-soluble). Occurs both as evaporite deposits in saline lakes and watercourses, or as bedded sedimentary deposits, or as salt domes.
Uses: Food seasoning and preserving meat.

 

Specimen: Creedite
Name origin: After the type locality, in the Creede quadrangle, Colorado.
Classification: Halides
Chemical Composition: Ca3SO4Al2F8(OH)2 · 2H2O
Color: White, violet, purple, colourless, orange; colourless in transmitted light.
Crystal structure: Monoclinic
Hardness: 4 Mohs scale
Specific Gravity: 2,713 to 2.73
Luster: Vitreous
Diaphaneity: Transparent
Streak: White
Cleavage: Perfect
Tenacity: Brittle
Fracture: Conchoidal
Source:
Uses:

 

Specimen: Sylvite
Name origin: From Latin “sal digestibus Sylvii”, salts of Sylvius, named after François Sylvius de le Boe (1614-1672), a physician and chemist of Leyden, Netherlands.
Classification: Halides
Chemical Composition: KCl
Color: Colorless, grey, white, yellowish to reddish, sometimes blue or violet.
Crystal structure: Isometric (cubic)
Hardness: 1.5 to 2 Mohs scale
Specific Gravity: 1.993
Luster: Vitreous
Diaphaneity: Transparent to translucent
Streak: White
Cleavage: Perfect
Tenacity: Brittle
Fracture: Irregular to uneven
Source: May deposit from volcanic gas, as shown in an experiment of Africano et al. (2002), in which it is a predominant precipitate at 550°C.
Uses:

 

Specimen: Atacamite
Name origin: Named in 1802 by Dmitri de Gallitzin after the type locality, in the Atacama Desert of northern Chile.
Classification: Halides
Chemical Composition: Cu2(OH)3Cl
Color: Bright green, dark emerald-green to blackish green; shades of green in transmitted light.
Crystal structure: Orthorhombic
Hardness: 3 to 3.5 Mohs scale
Specific Gravity: 3.745 to 3.776
Luster: Vitreous
Diaphaneity: Transparent
Streak: Apple-green
Cleavage: Perfect
Tenacity: Brittle
Fracture: Conchoidal
Source:
Uses:

 

Specimen: Octohedral Fluorite
Name origin: Named in 1797 by Carlo Antonio Galeani Napione from the Latin, fluere = “to flow” (for its use as a flux). The term fluorescence is derived from fluorite, which will often markedly exhibit this effect. The element fluorine also derives its name from fluorite, a major source of the element.
Classification: Halides
Chemical Composition: CaF2
Color: Purple, lilac, golden-yellow, green, colourless, blue, pink, champagne, brown.
Crystal structure: Isometric (cubic)
Hardness: 4 Mohs scale
Specific Gravity: 3.175 to 3.56
Luster: Vitreous to dull
Diaphaneity: Transparent
Streak: White
Cleavage: Perfect
Tenacity: Brittle
Fracture: Sub-Conchoidal and Spintery
Source:
Uses:

 

Specimen: Cubic Fluorite
Name origin: Named in 1797 by Carlo Antonio Galeani Napione from the Latin, fluere = “to flow” (for its use as a flux). The term fluorescence is derived from fluorite, which will often markedly exhibit this effect. The element fluorine also derives its name from fluorite, a major source of the element.
Classification: Halides
Chemical Composition: CaF2
Color: Purple, lilac, golden-yellow, green, colourless, blue, pink, champagne, brown.
Crystal structure: Isometric (cubic)
Hardness: 4 Mohs scale
Specific Gravity: 3.175 to 3.56
Luster: Vitreous to dull
Diaphaneity: Transparent
Streak: White
Cleavage: Perfect
Tenacity: Brittle
Fracture: Sub-Conchoidal and Spintery
Source:
Uses:

 

Specimen: Raw Banded Fluorite
Name origin: Named in 1797 by Carlo Antonio Galeani Napione from the Latin, fluere = “to flow” (for its use as a flux). The term fluorescence is derived from fluorite, which will often markedly exhibit this effect. The element fluorine also derives its name from fluorite, a major source of the element.
Classification: Halides
Chemical Composition: CaF2
Color: Purple, lilac, golden-yellow, green, colourless, blue, pink, champagne, brown.
Crystal structure: Isometric (cubic)
Hardness: 4 Mohs scale
Specific Gravity: 3.175 to 3.56
Luster: Vitreous to dull
Diaphaneity: Transparent
Streak: White
Cleavage: Perfect
Tenacity: Brittle
Fracture: Sub-Conchoidal and Spintery
Source:
Uses:

 

Specimen: Sliced Banded Fluorite
Name origin: Named in 1797 by Carlo Antonio Galeani Napione from the Latin, fluere = “to flow” (for its use as a flux). The term fluorescence is derived from fluorite, which will often markedly exhibit this effect. The element fluorine also derives its name from fluorite, a major source of the element.
Classification: Halides
Chemical Composition: CaF2
Color: Purple, lilac, golden-yellow, green, colourless, blue, pink, champagne, brown.
Crystal structure: Isometric (cubic)
Hardness: 4 Mohs scale
Specific Gravity: 3.175 to 3.56
Luster: Vitreous to dull
Diaphaneity: Transparent
Streak: White
Cleavage: Perfect
Tenacity: Brittle
Fracture: Sub-Conchoidal and Spintery
Source:
Uses:

 

Specimen: Cubic Fluorite
Name origin: Named in 1797 by Carlo Antonio Galeani Napione from the Latin, fluere = “to flow” (for its use as a flux). The term fluorescence is derived from fluorite, which will often markedly exhibit this effect. The element fluorine also derives its name from fluorite, a major source of the element.
Classification: Halides
Chemical Composition: CaF2
Color: Purple, lilac, golden-yellow, green, colourless, blue, pink, champagne, brown.
Crystal structure: Isometric (cubic)
Hardness: 4 Mohs scale
Specific Gravity: 3.175 to 3.56
Luster: Vitreous to dull
Diaphaneity: Transparent
Streak: White
Cleavage: Perfect
Tenacity: Brittle
Fracture: Sub-Conchoidal and Spintery
Source:
Uses:

 

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Data: Pellant, Chris. Smithsonian Handbooks: Rocks and Minerals, The clearest recognition guides avaiable. A Dorling Kindersley Book.

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