HomeChemical and Physical Properties of Jade

Chemical and Physical Properties of Jadeite and Nephrite

Jadeite is a silicate belonging to this group's inosilicate subdivision. Jadeite belongs to the pyroxene group of minerals within this subdivision, along with about two dozen other minerals (see Morimoto, Fabries, et al 1988; Hauff 1993: 85). The latter include aegirine, diopside, enstatite, and spodumene (hiddenite and kunzite). Curtiss (1993: 75) remarks that "the pyroxenes are one of the most complicated mineral groups known." Jadeite's chemical composition includes sodium, aluminum, and silicon. Jadeite's ideal composition is NaAl(Si203)2.

It can be described as "a sodium-rich aluminous pyroxene" (www.geo.utexas, pg. 1). Jadeitic pyroxene usually is not pure (pure jadeite being indicated as Jd100) and in such a state is found in only a few places in the world (discussed below). It is more typical for it to contain other pyroxenes mixed in solid solution such as diopside (CaMgSi2O6), kosmochlor (NaCrSi2O6), hedenbergite (CaFe2+Si2O6), and aegirine (NaFe3+Si2O6). Jadeitic pyroxene usually constitutes at least 90% to 95% of the rock that it is found in. The other minerals found in jadeite include sodic amphibole (with varying compositions: e.g., eckermannite, glaucophane, richterite, and edenite), albite, analcime, tremolite, (ilmeno-) rutile, clinochlore, banalsite, and chromite (see Harlow and Olds 1987; Htein and Naing 1994, and 1995). Ou Yang (1993) notes that jadeite may be partly replaced by fibrous tremolite or actinolite in the course of late-stage metasomatism. Such polymineralic jadeite is polychromatic and commonly is white with gray-green to blackish green specks or streaks. It is rare for this form of jadeite to be green and to exhibit relatively even color distribution. Jadeite commonly occurs with serpentine, nepheline, calcite, quartz, aragonite, glaucuphane, and vesuvianite. Jadeite's crystal system is monoclinic. It is composed of fine-grained, fibrous, highly inter-grown, interlocking crystals. Though jadeite is not very hard (measuring 6.5 to 7 on the Moh's scale), it is one of the toughest gem minerals known because of the inter-grown nature of the individual crystals. When fractured it is splintery and brittle. Jadeite ranges in appearance from opaque to translucent transparency and its luster from "greasy to pearly" (Hall 1994: 124).


Properties of Jadeite 



 

 

Jadeite

 

 

Nephrite

 

Chemical composition

NaAl(Si2O6) sodium aluminium silicate

Ca2(Mg,Fe)5Si8O22(OH)2calcium magnesium iron silicate

Crystal system

Monoclinic

Monoclinic

Cleavage

{110} good, (110):(110)~87°

{110} good, {100} parting; (110):(110) ~56°

Twinning

{100}, {001} simple, lamellar

{100} good; lamellar, common; {001} lamellar, rare

Optic character

Aggregate (DR)

Aggregate (DR)

Refractive index

1.666 - 1.680 (± 0.008); spot - 1.66

1.606 - 1.632 (+.009, -.006); spot - 1.60

Birefringence

usually not detectable

usually not detectable

Pleochroism

none (from GIA gemological data)

none (from GIA gemological data)

Ultraviolet Fluorescence

light green - inert to weak white (LW); generally inert (SW)

inert

 

light yellow - inert to weak green (LW); generally inert (SW)

 
 

white - inert to weak yellow (LW);

generally inert (SW)

 
 

light purple - inert to weak white or weak brownish red (LW); generally inert (SW)

 
 

some dyed lavender jadeite - moderate to strong orange (LW); weaker (SW)

 
 

dark colours - generally inert (LW and SW)

 

Absorption spectrum

Generally a line at 437nm; natural green - sequence of lines at 630, 655, 690nm; dyed green - a single broad band in the area occupied by the three lines in natural jadeite.

Rarely shows any absorption lines; a vague line may be visible at 500nm. Vague lines in the red end of the spectrum may rarely be seen in green stones of exceptionally quality.

Cause of Colour

green - chromium and/or iron;

lavender - iron (charge transfer);

yellow to brown - iron.

generally iron

Specific gravity

3.34 (+0.06, -0.09)

2.95 (+.15, -.05)

Polish luster

Vitreous to greasy

vitreous to greasy

Fracture

granular to splintery

splintery to granular

Luster

dull

dull

Identifying Characteristics

shiny reflections from individual crystals on unpolished backs of larger-grained stones

may have black inclusions

Crystal habit

massive

massive

Appearance

translucent to opaque

light to dark green, yellow to brown, white, lavender, blue and black.

translucent to opaque

light to dark green, yellow to brown, white, gray, black; often mottled

 

Name
Chloromelanite Jade 6.5+ 3.30-3.36 Monoclinic Imperfect 1.654-1.667 0.013 to None None None v Weak
Jadeite Jade 6.5+ 3.35 Monoclinic Imperfect 1.654-1.667 0.013 to None None None v Weak
Nephrite Jade 6+ 2.90-3.02 Monoclinic Lengthwise: perfect 1.600-1.627 -0.027 to none None Weak None

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