Garnets that display unique optical effects include Tanzanian and Madagascar Color Change Garnet, and Kamtonga Color Change Garnet from Kenya. Discovered in the 1970s, these examples are extracted from Umba-Tal (Tanzania), Bekyily (Southern Madagascar) and near Kamtonga (Kenya). The typical color change in these Garnets shifts from blue-green to purple-red, and from khaki green to orange red, and is caused by the high concentration of vanadium; occasionally, it is due to chrome, magnesium, manganese and iron compounds. Unfortunately, these Garnets with optical effects are only found in small sizes, which does not ruin their magic.
Chemical composition of Sphene
Sphene is a silicate of calcium and titanium, and owes its color to the presence of iron. Its color ranges from yellow-green to green and even brown hues. Due to its low hardness (5 - 5.5 on Mohs’ scale), it is a difficult gem to cut.
The principle Sphene deposit lies in Madagascar, but a few examples have also been extracted in Brazil, Canada, Mexico, Myanmar, Austria, Pakistan, Sri Lanka and the U.S. The raw material is extracted directly from the mother rock, also known as effusive rock.
The history of Sphene
This Titanium mineral was first discovered in 1795 in Hauzenberg, in the Bavarian forest. Sphene is a relatively new gemstone to the market, and thus has no myths or traditions associated with it.
A raw crystal of Capelinha Sphene
Properties of Sphene
The fire (dispersion of light into the colors of the spectrum) is greater than Diamond or Demantoid, and is always linked to the color of the gem: if the color is too intense, Sphene’s fire risks not being seen. The luster of Sphene is close to that of Diamond, and is referred to as ‘adamantine’ (‘similar to Diamond’). A not to forget the double refractivity, thanks to which light is split into two components, or rays, conferring great optical depth upon Sphene.
Its pleochroism also makes it appear as though Sphene changes color; this property causes diffracted light to display different colors depending on the angle of view.
Normally, Sphene is transparent and possesses crystalline purity - inclusions visible to the naked eye are rare, and disrupt its natural beauty.
Varieties of Sphene
One rare variety of Sphene is Capelinha Sphene, named for the Brazilian city famed for its mines. This variety of Sphene, with its unique lime green hue, also called Chartreuse, is among the most beautiful and most rare; currently, Sphene is no longer extracted from Capelinha.