GemID
Identify your gemstone.
ALEXANDRITE
Natural Chrysoberyl
Color change from yellowish, brownish, grayish, or bluish green in daylight or fluorescent light to orangy or brownish red to purplish red in incandescent light. Vitreous to subadamantine polish luster, conchoidal fracture with greasy to vitreous fracture luster.
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Might show fingerprints, angular included crystals, negative crystals,liquid inclusions, needle-like inclusions, or twinning
Key tests are appearance of color change, RI, pleochroism, and spectrum. Magnification separates natural from synthetic alexandrite. Warm colour change is mostly seen in Sri Lankan material.
R.I.
Bir.
1.746 to 1.755 (+0.004/-0.006)
0.008 to 0.010
DR
S.G
3.73 (+/-0.02)
9
LW
none, red
SW
none, red
BeAl₂O₄
orthorhombic
Brazil, Sri Lanka, Russia, Tanzania, India
Not commonly treated, oil filling possible.
AMAZONITE
Natural Feldspar
Light green to greenish blue, with mottled green and white grid-like patterns caused by two intersecting cleavage directions. Uneven to splintery fracture.
Mottled coloring with grid-like patterns
Key tests are appearance, RI, and fluorescence.
R.I.
Bir.
1.522 to 1.530 (+/-0.004)
0.008
AGG
S.G
2.56
7
LW
none, yellow, green
SW
none, yellow, green
KAlSi₃O₈
triclinic
Russia, China, Mongolia, South Africa, USA
Not commonly treated, resin waxing possible.
AMETHYST
Natural Quartz
Purple through violetish purple. Vitreous polish luster, conchoidal fracture with vitreous fracture luster.
Color zoning, liquid, two-phase, and threephase inclusions, negative crystals
Key tests are RI, birefringence, optic character, and optic figure. Magnification might separate natural from synthetic amethyst, but advanced testing might be required. Visual plotting might be necessary to separate amethyst from scapolite. Presence of Brazillaw twinning separates amethyst from scapolite with similar properties.
R.I.
Bir.
1.544 to 1.553
0.009
DR, AGG
S.G
2.66 (+0.03/-0.02)
7
LW
none
SW
none
SiO₂
trigonal
Brazil, Madagascar, Zambia, Namibia, Nigeria, Bolivia, Uruguay, USA, Canada, India, Sri Lanka.
Not commonly treated, heating, irradiation, and oil possible.
ANDALUSITE
Natural Andalusite
Yellowish green to brownish green and orangy brown. Due to strong pleochroism, both green and orangy pleochroic colors might be visible through the crown. Depending on cutting orientation, might appear brownish red. Vitreous
polish luster, uneven to conchoidal fracture with vitreous fracture luster. Distinct cleavage in one direction.
Needles (probably rutile) and crystals (probably apatite)
Key tests are RI, birefringence, optic character, and pleochroism.
R.I.
Bir.
1.634 to 1.643 (+/-0.005)
0.007 to 0.013
DR
S.G
3.17
7
LW
none
SW
none
Al₂SiO₅
orthorhombic
South Africa, Brazil, Sri Lanka,
Not commonly treated, oil filling possible.
APATITE
Natural Apatite
Vitreous polish luster, conchoidal to uneven fracture with vitreous fracture luster. Surface might show abrasions due to low hardness (Mohs 5).
Natural inclusions
Key tests are RI, birefringence, and optic character. Apatite’s low numerical RI is generally higher than the low numerical RI of tourmaline.
R.I.
Bir.
1.634 to 1.638 (+0.012/-0.006)
0.002 to 0.008
DR
S.G
3.18 (+/-0.05)
5
LW
none
SW
none
Ca5(PO4)3Cl
hexagonal
Myanmar (Burma), Brazil, India, Kenya, Madagascar, Norway, Sri Lanka, South Africa, Mexico, Canada and the United States
Not commonly treated, oil filling possible.
ALMANDINE
Natural Garnet
Generally dark-toned brownish orange to brownish red to purplish red hue with low saturation. Vitreous to subadamantine polish luster, conchoidal fracture with greasy to vitreous fracture luster. Large sizes might be
especially dark, and large gems are often cut shallow to compensate for dark tone. Cabochons might be cut in hollowback style for same reason.
Needle-like inclusions, usually intersecting at 70° and 110° angles in the same plane, high- and low-relief crystals, and zircon crystals with strain halos
Key tests are SR nature, and spectrum. Color is also helpful.
R.I.
Bir.
1.780 to OTL
none
SR
S.G
4.05 (+0.25/-0.12)
7
LW
none
SW
none
Fe₃Al₂Si₃O₁₂
cubic
Sri Lanka, East Africa, Australia, Brazil
Not commonly treated, oil filling possible.
AMBER
Natural Amber
Transparent to opaque. Light yellow to dark brown, orange, red, or white. Occasionally greenish or bluish due to strong fluorescence. Waxy to resinous polish luster, conchoidal fracture with waxy to resinous fracture luster.
Gas bubbles, flow lines, insects and other organic and inorganic inclusions. Plastic imitations with insect inclusions often show a boundary layer or “zone of encapsulation,” where an insect was inserted, then had fresh plastic poured over it. Treated material (heated with oil) shows disk-like fractures known in the trade as “sun spangles.”
Key test is SG. Amber generally floats in saturated salt solution (SG 1.13), while plastic (SG 1.30 +/-0.25) normally sinks.
R.I.
Bir.
1.540 (+0.005/-0.001)
none
SR
S.G
1.08 (+0.02/-0.08)
2
LW
none, yellow, green, orange, white, blue
SW
none, yellow, green, orange, white, blue
C 10 H 16 O
amorphous
Russia, Myanmar, Dominican Republic, Ukraine
Heating with oil.
AMMONITE
Natural Ammonite
Opaque gray to brown. Jewelry quality material displays iridescent colors. May show a spiral structure.
Distinctive, often iridescent, mosaic patterns
Key tests are appearance and possibly RI. Ammonite is the fossilized shell of an extinct animal. It is often polymer-impregnated to make it more stable or improve its appearance.
R.I.
Bir.
1.520 to 1.680
0.155
AGG
S.G
2.7
4
LW
Variable
SW
Variable
CaCO₃
amorphous
USA, Canada,
Often Resin impregnated.
ANDRATITE
Natural Garnet
Yellow to slightly greenish yellow or brown, with strong fire. Vitreous to subadamantine polish luster. Conchoidal to uneven fracture with vitreous fracture luster. Surface might show abrasions due to relatively low hardness (Mohs 6.5 to 7).
Natural inclusions
Key tests are OTL RI reading, lack of doubling, and spectrum. Sometimes sold as “topazolite” in the trade.
R.I.
Bir.
OTL
none
SR
S.G
3.84 (+/-0.03)
7
LW
none
SW
none
Ca₃Fe₃₊ ₂Si₃O₁₂
cubic
Iran, Italy, Russia, USA, Ukraine, East Africa, Sri Lanka