1.Mineralogical Characteristics

1)Mineral name: Celestite.

2)Chemical composition: (Sr,Ba)SO4. Sr content is greater than Ba content, may contain Pb, Ca, Fe and other elements.

3) Crystal system and crystallization habit: rhombohedral crystal system, rhombohedral bipyramidal crystals, plate-like crystals (see Figure 3-3-102). Intact crystals are rare, mostly stalactitic, nodular, fine-grained aggregates.

Figure 3-3-102 Columnar azurite crystals

4) Color: blue, green, yellow-green, orange or colorless.

5) Luster and Transparency: glassy luster, pearly luster on the cleavage surface; transparent.

6) Luminosity: biaxial crystal, positive luminosity.

7) Refractive index and birefringence: refractive index is 1.619-1.637; birefringence is 0.018.

8) Polychromy: weak.

9) Fluorescence: sometimes yellow or blue fluorescence under ultraviolet light.

10) Absorption spectrum: insignificant.

11) Decomposition and fracture: two groups are completely decomposed.

12) Mohs hardness: 3 to 3.5.

13) Density: 3.87 to 4.30g/cm3.

2. Gemological Information

Blue color is more precious, followed by green, orange, yellow, and colorless transparent ones. Transparent clusters can be collectors' items without processing. Single crystals are generally processed into stepped or curved, less than 3 ct in size, due to the hardness of the small, should not be used as jewelry, mostly for the collection.

In Canada, there are 20.1ct of blue treasures collection.

3. Production and origin

Mainly from sedimentary rocks, especially dolomite and dolomitic limestone, but also in hydrothermal veins. Gem-quality crystals are produced in Lake Erie in North America, and are also found in Canada, Namibia, Mexico, the United Kingdom, France, Italy, and so on.