Useful information
About noble metals
Properties and definitions about
gemstones
Chemistry and physics of gemstones
About the minerals and gemstones in
the quarts group
Gemstones in the corundum group -
rubines and saphires - down at this page
Beryl group gemstones, garnets, topaz - down at this page
What characterizes dive watch - down at this page
Tourmaline group gemstones
Lapiz lazuli
How does gemstones get their colours
About perls and nacre
About garnets
Garnets are stones that form
natural cubic or rhombic crystals, colored mostly dark red, but any other color
is also found. The crystals are often found stuck together to roundish objects,
and these objects or single crystals are usually trapped iniside rocks of
various kind, often hard rocks of igneous or metamorphic kind.
Garnets can be transparent and
these are used as gemstones. Garnets are concidered the gemstone for january.
Usually single crystals of good quality are used, but also stones consisting of
many small garnet tightly packed crystals are used. Often garnets are only
translucent or opaque. These others are used industrially as abrasive material.
The chemical composition varies,
but with silicate as a constant ingredient. The general formula is
X3Y2(SiO4)3.
The variable components are often iron, magnesium, calcium, aluminium, manganese
and cromium. The X usually constitutes divalent cations (Ca2+, Mg2+, Fe2+) and
the Y usually trivalent cations (Al3+, Fe3+, Cr3+) in an octahedral/tetrahedral
structure with [SiO4]4− occupying the tetrahedra
Common variants are these:
Pyrope Mg3Al2Si3O12, Almandine Fe3Al2Si3O12, Spessartite Mn3Al2Si3O12 ,
Andradite Ca3Fe2Si3O12 , Grossular, Ca3Al2Si3O12, Uvarovite Ca3Cr2Si3O12 .
The exact color and hardness depend upon the composition. They have the hardness
grade 6.9 - 7.5. Some garmets change color depending on the angles it is
illuminated and seen from.
What is a diver watch or dive watch
There are several characteristics that distinguish
a dive watch from other watches.
A dive watch is water tight, and this thightness
holds in pressure up to at least 10 ATM.
A dive watch is also made of materials that are
not corroded, miscolored or otherwise disturbed by water and salt, for exampkle
stainless steel and chromium.
A dive watch have some arrangement, so that the
time elapsed from a certain start point can be measured. On way of doing this is
by having one or two bezels around the watch perifery with figures that can be
used to count number of seconds, minutes or hours from a zero point. A beazel is
rotated so that the zero points are aligned at the places where a pointer of the
watch is, and after this the pointer will point at the figure on the beazel
showing elapsed time.
More advanced dive watches can have stop clock
functions with pointers that move by themselves and show elapsed time.
Digital dive watches will typiclly have digital
stop clock function showing elapsed time form some point.
Dive watches will also have figures in colors that
easily are seen in the light conditions deep into the water, or have self
illuminating figures.
Advanced dive watches can also have in-built
measurment of pressure and depth level, and logging functions.
The beryl group of gemstones
Minerals in the beryl group are silicates of beryllium and aluminium, having the chemical formula Be3Al2(SiO3)6 Beryl is found as barrel-formed crystals.
The hardness of the crystals are of the grade 7.5 - 8.0.
Beryl is usually found in granitic pegamitic rocks. The crystals of beryl are six-sided or hexagonal columns.
Beryl often contain disolved elements giving colour to the crystal. Beryl without distinct inclusions and without uneven colour are used as gemstones. Beryl not of gemstone quality is most often called only beryl. There are the following types of beryl gemstones differing in their colour:
Emerald: This is deep green beryl. Larger specimens without easily visible inclutions of foreign materials are rare and expensive. The colour is produced by cromic oxide dissolved in the crystal substance. Vanadium and iron may also effect the colouring shade.
Aquamarine: Aquamarine means sea water. The colour is skyblue, sea blue or greenish blue. The colour is due to traces of iron in the crystal framework.
Morganite: This variant has a pink color. It is an extreemely rare and expensive stone.
Bixbite: This is red beryl. Like morganites, specimens are rare and expensive.
Golden beryl: This variant is golden yellow.
Goshenite: This is coluorless beryl. It is found at the place Goshen in massechusets. Even though the variant is rare, the value is moderate due to lack of optical refractive brilliance.
To see emerald pieces, please scroll up.
The topaz group of gemstones
Minerals in the topaz group are hydroxy-fluoro-silicates of aluminium, having the chemical formula Al2(OH,F)2SiO4 , with varying ratio between the hyroxy- and fluorine components. Beryl is found as crystals of 6 sides with 90 degree angles -ortho-rhombic crystals.
The hardness of the crystals are of the grade 8.0. The crystals can easily be cleaved in one plane, and unfortunate impacts on the stone can easily let the stone brake along the cleavage direction.
The place of origine of topaz are mostly Brazil, Nigeria, and Burma
Yellow topas: The color varies from yellow to yellowish brown. There is water in the crystal composition responsible for this colour.
Blue topaz: Blue topas are found in nature, but mostly blue topaz is produced by heating and irradiation of stones having other colours. The colour can vary from pale blue ( London Blue), through medium blue (Swiss Blue) to deep blue (Sky Blue). Topaz of this colour has less water and more fluorine in the crystal framework.
Red topaz : There are also orange or red topazes. These stones contain cromium and are usually treated by heat.
To see topaz pieces, please scroll up.