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The current featured stone:

 

Sapphirine

 

Refractive Index:  1.701-1.718 Crystal Structure: Monoclinic
 

 

 
Hardness:  7.5 Specific Gravity:  3.4-3.5
 

 

 
Chemical Composition:  (Mg,Al)8(Al,Si)6O20
 
Occurrences:   Sri Lanka, Tanzania, Madagascar

Sapphirine is an uncommon silicate mineral that owes it's unusual name to the fact that its color range can overlap that of Sapphire.  This is the most common hue of Sapphirine is a deep greenish-grayish blue that is often fairly dark in tone.  Sapphirine also has a very strong directional color and this pleochroism often gives finished gems flashes of a copper color hue.  Have a look at the keystone cut stone in the photo below for a good example of this.

Though Sapphirine clearly falls into the "rare stone" category, it is a relatively durable stone with a Moh's hardness of 7.5.  This makes it one of the few rare stones which are capable of being used in jewelry and admired as more than a gem confined to a case or stone paper.  The traditional locality for gem grade Sapphirine (despite the fact that the type locality is in Greenland) has always been Sri Lanka and the few gems that are on the market have often come from the deposits around Kolonne, Sri Lanka.

While the distinctive blue color is the most common, there are examples that go beyond this.  Notably, there have been a few primarily purple stones that come from the same area in Sri Lanka - see the oval stone below.  These also tend to be fairly dark in tone while having a less evident pleochroism face-up.

Most recently some of these purple stones as well the more familiar blue pieces have been coming from E. Africa.  Tanzania has been seeing some production of gem Sapphirine and has even expanded the gem's color range a bit more - a very unusual brownish-red color has been documented from this locality.  Some of the stones from this deposit have been extremely large for the species as well - gem Sapphirine rarely exceeds one carat in most finished pieces, but several stones of over five carats have been seen from Tanzania. 

Sapphirine's very distinctive appearance along with their somewhat unusual durability have made them fairly popular with collectors.  Stones have been always been in demand with fans of rarer colored stones and with the new possibility of unusual colors and larger stones, that interest may be poised to expand.