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Iolite
Mg
2Al
4Si
5O
18 Magnesium Aluminum Silicate
Iolite Appearance
Iolite is generally seen as a deep blue stone when faceted and set
in jewelry, but it displays an exceptional pleochroism that causes the
stone to appear as one of three distinct colors depending on the angle
it is viewed from. The stone may be seen as violet blue, yellow gray
or a light blue based on the axis. The strong distinction in color
based on angles must be taken into account by the cutter in order to
produce the deep violet blue that is expected of the finished gem.
Iolite is transparent and is generally free of inclusions that can be
seen by the naked eye. Also known as cordierite or dichroite, it has
also been referred to as a water sapphire.
Iolite Occurrence
Iolite comes from Sri Lanka, India, Madagascar, Burma, Zimbabwe,
Brazil, Canada and the US.
Physical Properties of Iolite
| Composition
| Mg2Al4Si5O18
| Class
| cyclosilicates
|
| Specific gravity
| 2.68 - 2.80
| Refractive Index
| 1.52 to 1.57
|
| Birefringence
| weak (.008 to .012)
| Pleochroism
| very distinct
|
| Cleavage
| imperfect
| Fracture
| subconchoidal
|
| Luster
| vitreous
| Transparency
| transparent to translucent
|
| Streak
| white
| Fluorescence
| None
|
| Crystal system
| Orthorhombic
| Twinning
|
|
| Hardness
| 7.0 - 7.5
| Dispersion
| .017
|
| Color
| Depending on the viewing angle the color will
change from blue or blue-violet to yellowish gray to light blue.
|
Images © theimage.com
| Crystal habit
| Usually massive, or in compact grains embedded in
metamorphic schists and gneisses, but often as pebbles and grains
in alluvial deposits. Rarely as prismatic crystals.
|
Other
| One of the most notable physical properties of
iolite is its extremely strong pleochroism, or color changing
ability.
|
Formation of Iolite
Iolite is formed in igneous rocks and pegmatite intrusions. It is
a complex magnesium aluminum silicate, with the magnesium partially
replaced by ferrous iron and manganese, and the aluminum replaced
partially by ferric iron.
Iolite History
The name 'Iolite' comes from the Greek words "ios" meaning violet
and "lithos" meaning stone. The origin of the reference to iolite as
a 'water sapphire' is unsure, but thought to date back to the
Vikings who used it as a navigational aid. When cut in thin slices,
the extreme pleochoism of the stone may be used as a polarizing
filter. With the aid of this filter, the exact position of the sun
may be determined, even on overcast days.
Iolite Lore
Iolite is said to increase spiritual insight and help in seeing
both sides of an issue more clearly.
Copyright © 2005 by Gem And Mineral Info.com.
All descriptions and images, except where noted, are the property of
Gem And Mineral Info.com
Where noted images and descriptions are used with permission of copyright
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