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Gems & Gemmology

ACTINOLITE

Description:
Nature of Material: Mineral species; monoclinic crystal system; chemical composition Ca2(Mg,Fe)5Si8O22(OH)2

Appearance:

  • Usually translucent light to dark green, yellowish green, black.

Hardness : 5 to 6
Variety and Trade Names:

  • Cat’s-eye Actinolite – translucent to opaque green to yellowish green, with chatoyancy (Cat’s eye)

AMBLYGONITE

Description:
Nature of Material: Mineral species; triclinic crystal system; chemical composition (LI,Na)Al(PO4)(F,OH); belongs to a solid solution series with montebrasite; most gem specimens lie closer to the montebrasite end

Appearance:

  • Transparent
  • Usually colourless to light yellow or golden yellow, greenish yellow; may be light pink, green, blue, brown, or purple
  • Phenomena: none

Hardness : 51/2 to 6
Toughness: poor
Variety and Trade Names: None


ANDALUSITE

Description:
Nature of Material: Mineral species; orthorhombic crystal system; chemical composition Al2SiO5

Appearance:

  • Transparent to opaque
  • Usually brownish or yellowish green to orangy brown (both green and orange pleochroic colours often visible through crown); may be pure green, brown, pink, and violet.
  • Phenomena: none

Hardness: 7 to 71/2
Toughness: fair to good
Variety and Trade Names:

  • Chiastolite – translucent to opaque with a dark cross-like pattern on a white, gray reddish, or light brown background.

APATITE

Description:
Nature of Material: Mineral group; hexagonal crystal system; chemical composition Ca5(PO4)3(F,OH,Cl);

Appearance:

  • Transparent to translucent
  • Yellow, green, violet, purple, blue, pink, brown, colourless

Hardness: 5
Toughness: fair
Variety and Trade Names:

  • Cat’s-eye – semi-transparent to translucent, usually green or yellow bodycolor, with chatoyancy (Cat’s eye).

ARAGONITE

Description:
Nature of Material: Mineral species; orthorhombic crystal system; chemical composition CaCo3(carbonate)

Appearance:

  • Colourless, white, grey, red, yellow, brown, green, blue, violet; colored varieties usually light in tone

Hardness : 3 1/2 to 4
Toughness: fair to poor
Variety and Trade Names: None


ASSEMBLED STONES

Description:
Nature of Material: Manmade imitations constructed from any combination of natural and/or manmade materials;

Appearance:

  • All colours
  • Phenomena: varies, all are possible

Cleaning Methods:

  • ultrasonic: never
  • steamer: never
  • warm soapy water: usually safe

AXINITE

Description:
Nature of Material: Mineral group; triclinic crystal system; Chemical composition (Ca,Fe,Mn,Mg)3Al2BSi4O15(OH); Mineralogists sometimes specify various group members as Magnesioaxinite, ferroaxinite, or manganaxinite, depending on chemical composition

Appearance:

  • Transparent to translucent brown, purplish brown, brownish yellow, violet, and blue.

Toughness: poor to fair
Variety and Trade Names: None


AZURITE

Description:
Nature of Material :Mineral species; monoclinic crystal system; chemical
composition Cu4(CO3)2(OH)2

Appearance:

  • Usually semi translucent to opaque, rarely transparent dark blue to violetish blue

Hardness: 3 1/2-4
Toughness: poor
Variety and Trade Names: None


AZURMALACHIT

Description:
Nature of Material :Rock composed of azurite and malachite

Appearance:

  • Opaque; Patterned in blue and green

Hardness: 3 1/2-4
Toughness: poor

  • ultrasonic: never
  • steamer: never
  • warm soapy water: safe

BARITE

Description:
Nature of Material: Mineral species; orthorhombic crystal system; chemical composition BaSO4;

Appearance:

  • Transparent to opaque
  • Colorless,pink,red,yellow,green,blue,brown
  • Phenomena: none

Hardness : 3 to 31/2
Toughness: poor
Variety and Trade Names:

  • Desert roses - aggregate rosette forms

BENITOITE

Description:
Nature of Material: Mineral species; hexagonal crystal system; chemical composition BaTiSi3O9

Appearance:

  • Transparent
  • Blue, violetish blue, colourless or white; pink(rare)
  • Phenomena: none

Hardness : 6 to 61/2
Toughness: fair
Variety and Trade Names: None


BERYL

Description:
Nature of Material: Mineral species; hexagonal crystal system; chemical compostion Be3AL2Si6O18

Appearance:

  • Transparent to opaque
  • Colorless, green,yellow,light orange,pink,red(rare),blue(fading Maxixe type), Brown,black
  • Phenomena: chatoyancy (cat’s eye), asterism (star)

Hardness : 71/2 to 8
Toughness: good

Cleaning Methods:

  • ultrasonic: risky
  • steamer: risky
  • warm soapy water: safe, but avoid strong detergents and vigorous scrubbing of plastic coated stones

Variety and Trade Names:-

  • Bixbite - Raspberry red
  • Green beryl - green variety whose color is too light, desaturated, or yellowish to be called emerald.( very strongly bluish green through yellow- green )
  • Heliodor - greenish yellow to orange or yellowish brown
  • Morganite - pink
  • Goshenite - colorless
  • Cat’s-eye beryl - various bodycolors, with chatoyancy (Cat’s eye)
  • Star beryl - typically dark yellowish brown to black, with asterism (usually 6 rays and weak)
  • Aquamarine - greenish blue to blue-green, generally light in tone. Phenomena: chatoyancy (Cat’s eye)
  • Emerald - very strongly bluish green through green. Phenomena: chatoyancy , asterism.

NOTE: Synthetic beryl- various bodycolors

NOTE: Plastic coated beryl- various bodycolors


EMERALD beryl

Description:
Nature of Material: A variety of the mineral species beryl (BARE-ul); hexagonal crystal system; chemical composition Be3Al2Si6O18

Appearance:

  • Light to very dark green to very strongly bluish green

Variety and Trade Names: (See Beryl)

Enhancements:

Method: oiling is commonly used in enhanced emeralds in the trade (oil may contain green dye)
Effect: hides flaws, improves transparency, may deepen color

NOTE: The Comment will be: Evidence of oil like substances, are commonly used in enhanced emerald.

NOTE: Synthetic Emerald are available in the trade (See Beryl)
NOTE: Plastic coated Emerald (beryl)- are available in the trade (See Beryl)


SYNTHETIC EMERALD (synthetic beryl)

Description:
Nature of Material: synthetic emerald is a man-made material with essentially the same chemical composition and crystal structure as natural emerald; see Emerald.

Appearance:

  • Transparent
  • Medium to medium dark green to bluish green
  • Phenomena: none

Cleaning Methods:

  • ultrasonic: risky
  • steamer: never
  • warm soapy water: safe

Toughness: slightly tougher than most natural emerald

NOTE: Synthetic Emerald are available in the trade (See Beryl)


BRAZILIANITE

Description:
Nature of Material: Mineral species; monoclinic crystal system; chemical composition NaAl3(PO4)2(OH04

Appearance:

  • Transparent to translucent
  • Yellowish green to greenish yellow, rearely colorless
  • Phenomena: none

Hardness : 51/2
Toughness: poor to fair

Variety and Trade Names: None


CALCAREOUS CONCRETIONS

Description:
Nature of Material :Chemical composition is mostly CaCO3,plus some organic matter and water; calcareous concretions include:

Appearance:

  • Translucent to opaque (Various colors)
  • Distinctive flame-like sheen on conch and tridacna pearls

Hardness: 21/2 to 4
Toughness: fair to poor


CALCITE

Description:
Nature of Material: Mineral species; hexagonal (trigonal) crystal system; chemical composition CaCO3

Appearance:

  • Transparent to opaque
  • Almost all colors

Hardness : 3

Variety and Trade Names:

  • Iceland spar – transparent colorless
  • Marble – granular aggregate occurring in many colors
  • Onyx marble – banded marble

NOTE: Dyed to improve color

NOTE: Plastic impregnation to improve appearance of polish


CASSITERITE

Description:
Nature of Material: Mineral species; tetragonal crystal system; chemical composition SnO2

Appearance:

  • Transparent to opaque dark brown to black, yellowish brown, yellow or colorless banded with brown

Hardness : 6 to 7
Toughness: fair to good


CHALCEDONY

Description:
Nature of Material: Microcrystalline or crytocrystalline quartz; hexagonal (trigonal) crystal system; chemical composition SiO2

Appearance:

  • Virtually all colors

Hardness: 61/2 to 7
Toughness: good

Variety and Trade Names:

  • Milky - white to gray
  • Chrysoprase - light to medium yellowish green (natural color) material does not apply to dyed green.
  • Carnelian - orange, brownish-orange, brownish-red to orangy red to red.
  • Prase - grayish green
  • Bloodstone or Heliotrope - dark green with brownish red spots of color.
  • Moss Agate - colorless, white, or gray, with moss like inclusion (commonly green).
  • Onyx - parallel layers or band of color;
  • Sard - darker and less saturated than carnelian
  • Agate - curved or irregular banding; any color or combination of color.
  • Sardonyx - onyx with bands of sard or carnelian colors alternating with white and /or black layers.
  • Jasper - any color or combination of colors, except black or bloodstone color.
  • Chrysocolla in chalcedony - blue to green-blue;colored by inclusion of the copper mineral chrysocolla;
  • Petrified wood - wood that has been entirely replaced by chalcedony;it resembles a patterned jasper
  • Iris agate - spectral color along a typical botryoidal agate structure when light is transmitted through a thin section.
  • Fire agate - dark orange-brown to brown with a botryoidal structure; exhibits iridescent along that structure.
  • Dendritic agate - colorless, white, or gray, with dendrites or tree-like inclusion.

NOTE:The trade also refers to opaque, solid black chalcedony as onyx or black onyx.

  • Dyed to alter color
  • Heating to produce orange or orangy red from yellow to brown material

Enhancements:

Method: dyeing:

NOTE: The Comment will be: Evidence of a applying artificial external surface color or dyeing.

Enhancements:

Method: heating:

NOTE: The Comment will be: None


CHRYSOBERYL

Description:
Nature of Material: Mineral species; Orthorhombic crystal system; chemical composition BeAl2O4

Appearance:

  • Light to medium yellow to yellowish green, grayish green, brown to yellowish brown, light blue (rare)
  • Phenomena: see following entries on Alexandrite and Cat’s-Eye

Hardness : 81/2

Variety and Trade Names:

  • Cat’s eye chrysoberyl:
  • Alexandrite:(See Alexandrite)

Appearance:

  • Yellow to yellowish green, grayish green, brown to brownish yellow
  • Phenomena: chatoyancy (cat’s eye) cases of 4-ray asterism(star) instead of Chatoyancy (cat’s eye)

Appearance: (Alexandrite)

  • Daylight: yellowish, brownish, grayish or bluish green; incandescent light: orangy or brownish red to purple-red
  • Phenomena: color change, may also show chatoyancy(cat’s eye)

NOTE: Synthetic Alexandrite are available in the trade (See Alexandrite chrysoberyl)


ALEXANDRITE chrysoberyl

Description:
Nature of Material: alexandrite is the color change variety of the mineral species chrysoberyl (see chrysoberyl)

Appearance:

  • Daylight: yellowish, brownish, grayish or bluish green; incandescent light: orangy or brownish red to purple-red
  • Phenomena: color change, may also show chatoyancy (cat’s eye)

Variety and Trade Names:

  • Cat’s-eye Alexandrite - very rare variety with both chatoyancy and color change

NOTE: Synthetic Alexandrite are available in the trade (See chrysoberyl)

Hardness : 8 1/2
Toughness: excellent