A stunning specimen of bright blue Lazurite Crystals on Calcite with Pyrite. Or, in other words, deconstructed Lapis Lazuli! One extra large crystal dominates the specimen, with some partial crystals visible in the matrix. This is a very collectible piece and a beautiful example of Afghanistan’s rich mineral wealth. Great colour splash for the collection. This specimen stands well on a perspex display pad.
4cm x 2.4cm x 2cm, 14g.
Sodium Calcium Aluminum Silicate Sulfur Sulfate
(Na, Ca)8Al6Si6O24(S, SO4)
Group: Both the Sodalite and feldspathoid groups.
Uses: mineral specimens and ornamental stones
Lapis Lazuli or Lapis for short is mostly Lazurite but commonly contains pyrite and calcite and some other minerals. The name means “blue rock” and is always a brilliant blue with violet or greenish tints. The rich blue color is due to the sulfur that is inherent in the structure of Lazurite. Small crystals of pyrite are always present in Lapis. Their brassy yellow color helps in distinguishing Lapis from its also blue cousin Sodalite. Sodalite rock has no Pyrite. The calcite produces white streaks in the Lapis and too much calcite will lower the value of the stone.
Lapis Lazuli first mined 6000 years ago and still is today in Kokcha, Afghanistan. Europeans even ground down the rock into an expensive powdered pigment for paints called “ultramarine”. Although now not the only source of Lapis, the source in Afghanistan still produces the finest quality material.
Lazurite is a member of the feldspathoid group of minerals. Found in silica poor rocks containing silica poor minerals and no Quartz. If quartz were present when the melt was crystallizing, it would react with any feldspathoids and form a feldspar. Localities that have feldspathoids are few.
Color is brilliant blue with violet or greenish tints.
Luster is dull to greasy.
Transparency: Crystals are translucent to opaque.
Crystal System: Isometric; bar 4 3/m
Crystal Habits: Dodecahedral crystals are rare, usually massive as a rock Lapis Lazuli forming mineral.
Cleavage is poor, in six directions, but rarely seen.
Fracture is uneven
Hardness is 5 – 5.5
Specific Gravity is 2.3 – 2.4 (somewhat below average)
Streak is bright blue.
Other Characteristics: Index of refraction is 1.5.
Associated Minerals calcite, some pyroxenes and most diagnostic pyrite.
Notable Occurrences include Kokcha River valley, Afghanistan; Ovalle, Cordillera, Chile; near Lake Baikal, Russia; Mt. Vesuvius, Italy; Cascade Canyon, San Bernardino Mountains and Ontario Peak, California and in the Sawatch Mountains, Colorado, USA.
Best Field Indicators are the violet-blue color, pyrite association (unlike Sodalite), locality and specific gravity.