What is Lapis Lazuli?

Single, natural, isometric, 1 inch
crystal of lazurite (lapis lazuli) from near Badakshan, Afghanistan
Scanned photograph taken from The Gem
Kingdom by Paul E. Desautels, Random House, Inc. New York.

Lapis lazuli is an opaque gem stone  that may range in color from brilliant, to medium royal, to dark blue.  Its composition consists of a mixture of several different minerals including,  the predominance of lazurite (25-40%), hüaynite, sodalite, noselite, calcite and pyrite.  Small amounts of  diopside, augite, mica and hornblende  may also be present.  Lapis lazuli generally occurs in crystalline limestone as the result of contact metamorphism.

Lapis lazuli gets its brilliant blue color from its sulfur content.  The more evenly the color is distributed throughout the stone, the higher  the quality, and the greater the value.  Lapis generally occurs with a speckled and strained consistency, with glittering inclusions of iron pyrite.  If the pyrite is well distributed, the stones  beauty may be  enhanced adding to its genuineness.
 
 


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Scanned photograph taken from
Gemstones of the World,
Schumann (1997), p. 173.

Too much pyrite however may cause the  stone to have a dull greenish tint.  The most costly and precious form of lapis lazuli is mined in Afghanistan,  having a rich uniform deep blue color, and little to no white calcite veining (which may diminish the value), as well as only  a few flecks of glittering pyrite.   Lesser quality lapis lazuli is mined in Chile (Chile lapis) and also in Russia.  Lapis mined from these areas generally has a strong whitish or gray color thus diminishing its value.  Some smaller deposits of the stone have been  found in Argentina, Burma, Canada, and the United States as well (Schumann, 1997, p. 173)
 
 

PHYSICAL PROPERTIES
Lapis Lazuli chemical composition
Lazurite:  (Na,CA)8(AlSiO4)6(SO4,S,Cl)2
Haüynite:  (Na,CA)4-8(AlSiO4)6(SO4)1-2
Sodalite:   Na8[Cl2(AlSiO4)6]
Nosean:   Na8(AlSiO4)6SO4
Calcite:    CaCO3
Pyrite:      FeS2
 Habit compact massive
 Index of refraction approximately 1.5
 Pleochrosim none (isotropic)
 Specific Gravity generally 2.7 to 2.9, higher with increasing pyrite content
 Hardness 5.0 to 5.5
 Color deep blue, purplish blue, or greenish blue
 Luster dull
 Transparency translucent
 Cleavage none
 Fracture uneven
 Streak light blue
Table information taken from http://www.mineralminers.com/html/lapminfo.htm

Lapis stone is often imitated by adding dyes to a variety of other stones or synthetic materials.  The dying process may also be used in combination with the crushing of a less valuable grade of lapis lazuli and then reconstituting it back together.  The presence of iron pyrite deposits within a lapis lazuli specimen would indicate that is most likely authentic, and has not been reconstituted.
 

Caring for lapis lazuli

Because lapis lazuli is rather porous, it should never come in contact with chemicals and solvents.  The best way to clean the stone is with mild, warm, soapy water.   Lapis, having only the  hardness of 5 to 5.5  should be protected from rubbing and scratching against harder stones and surfaces, such as other jewelry within a jewelry box.
 


The material for this section was taken primarily from:


 

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