Jadeite

Hand Specimen identification: Association with other high-pressure minerals, form, two (rarely seen) cleavages at near 90°, green color, and tenacity identify jadeite. It is distinguished from nephrite by its luster. An optical microscope may be needed to confirm identification.

Chemical Composition : NaAlSi2O6

Hardness : 61 2 to 7

Specific Gravity3.3

Cleavage/Fracture : two perfect {110}/uneven

Luster/Transparency : vitreous, greasy/translucent

Color : variable shades of greento white

Streak : white

Optical Properties : Jadeite is colorless to very pale green in thin section. Birefringence is low; anomalous blue interference colors are common, maximum interference colors are first-order red or yellow. Jadeite exhibits typical clinopyroxene shape and cleavage but has a higher 2V than most. Biaxial 1+ 2, a = 1.65, b = 1.66, g = 1.67, d = 0.02, 2V = 70° to 75°.

Crystallography : Monoclinic, a = 9.50, b = 8.61, c = 5.24, b = 110.46°, Z = 4; space group C2/c; point group 2/m.

Habit : Jadeite is usually granular, forming tenacious masses; less commonly, in prismatic or tabular crystals.

Structure and composition : Jadeite is similar in structure to other clinopyroxenes and may contain some of the same impurities (see diopside). It forms limited solid solutions with aegirine, NaFeSi2O6, with omphacite, 1Ca,Na21Fe,Mg,Al2Si2O6, and with other pyroxene end members.

Occurrence and associations : Jadeite is a high-pressure pyroxene found in metamorphic rocks of the blueschist facies. It is associated with other high-pressure minerals such as glauco-phane, lawsonite, or aragonite, and with quartz and epidote. A bright green variety of jadeite, omphacite, occurs in eclogites with pyrope-rich garnet. Omphacite is also found in kimberlites.

Varieties :

Related Minerals : Jadeite is closely related to other Na-pyroxenes: aegirine, NaFeSi2O6; omphacite, 1Ca,Na21Fe,Mg,Al2 Si2O6; and aegirine-augite, 1Ca,Na21Fe12+,Fe23+,Mg2Si2O6. It is chemically similar to nepheline, Na,K AlSiO4, and to albite, NaAlSi3O8.

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