Amethyst facts - another perspectiveBy: Nandita Ray
Summary: Amethyst is a crystal. Crystals are built out of atoms. Atoms are made up of protons, neutron and electron. When the atoms of a mineral are arranged in a particular manner i.e. the mineral has a definite internal order due to the periodic arrangement of atoms in three dimensions, it is called a crystal.
Amethyst is a crystal. It falls in the quartz group of minerals. It is
the purple variety of quartz Si02. It comes in various shades of purple. It
is a mineral gemstone, growing in rocks found on the surface of the earth.
It is considered a precious stone. Minerals can only be identified by x-rays
and chemical tests. These tests help determine the structure and the
chemical composition of the mineral.
Formation: The presence of manganese in quartz leads to purple amethyst.
While yellow quartz is said to be burnt amethyst. If exposed to extreme
heat, amethyst turns yellow. Ferric thiocynate and even sulfur was detected
in this mineral. Amethyst usually forms as clusters of crystals. Quartz is
silicon dioxide. It is a silicate. Amethyst is a polymorph of silicon
dioxide and its other eight structures are called quartz. All members of
this group are rare except for the quartz. Quartz is the most common mineral
found easily in any environment and is a part of every rock type.
Such crystals grow in the cavities or holes in the rocks. Sometimes it forms
a lining inside the narrow veins of the parent rock or in geodes. A geode is
a huge hollow which contains a crop of amethyst crystals growing inside it.
As water seeps or flows through these rocks and cavities, interaction
between the minerals present in the rock and in the running water takes
place and due to this chemical reaction, the crystals of amethyst is formed.
Water is composed of water molecules. Though the molecules are tightly
packed, they do not stick together. They do not form any rigid structure and
therefore water has no fixed shape and takes the shape of the container. How
ever it resists compression. If the temperature is drastically reduced, a
marked change takes place in the physical character of the water. Under
close microscopic examination it is found that the molecules suddenly align
with one another to make a rigid hexagonal lattice. It can now hold a fixed
shape. This leads to the formation of crystal.
Water which is flowing over the minerals present in the rock interacts with
these minerals. If the solution thus formed, under goes a temperature
change, the solution will either evaporate or cool down. The mineral present
in it will precipitate. (Example- the formation of salt crystals due to
evaporation of sea water) The mineral that is formed is due to the dissolved
elements in the water and the minerals present in the rocks. If the rock has
silica which is sandstone, amethyst will be formed. The chemical reaction
between silicon and oxygen leads to the formation of amethyst. Water plays
an important part in the formation and it is usually rain water that carries
many dissolved minerals in it. When the water evaporates, the silica gets
left behind in form of crystals, in cracks and hollows of the parent rock.
Amethyst is a crystal. Crystals are built out of atoms. Atoms are made up of
protons, neutron and electron. When the atoms of a mineral are arranged in a
particular manner i.e. the mineral has a definite internal order due to the
periodic arrangement of atoms in three dimensions, it is called a crystal.
Regular forms of large crystals show internal atomic order. Amethyst can
occur as long prismatic crystals that are crystalline crusts and have
pointed ends called druses. Amethyst can also occur as six sided pyramids at
either ends. Crystals having well developed crystal faces are called
euchedral. Crystals do not always have well developed faces. Crystals must
have the negative and positive charges balanced. Silicate minerals have
structures having enough silica (sand) tetrahedral i.e. a tetrahedron with a
Si at the center, surrounded by four oxygen anions. Many silicates contain
linkages of silica tetrahedral. This is the core of the structure. Silicates
minerals are divided based on the position of the tetrahedral formation.
Example-amethyst, in which tetrahedron is linked to four other tetrahedral,
making a cross linked framework. Amethyst crystals can be hexagonal, can be
tall prismatic crystals or can be short and stubby ones.
Sometimes amethyst is also formed when red hot magma i.e. molten rock seeps
into the crevices and hollows of a parent rock and gets cooled. It is a
complex high temperature silica solution with temperature ranging from
600-1200 degree centigrade. It is under high pressure and is composed of
silica and iron. As the magma cools, crystallization of the water rich magma
containing lots of rare elements and volatilities fills up the cracks and
quartz is formed as gem crystals. Quartz is a low pressure temperature
polymorph of SiO2. It is composed of irregular superposition of alternate
lamella of right handed and left handed quartz. This is believed to be due
mechanical stresses. As a result, amethyst easily breaks up in a rippled
fracture.
Amethyst crystals can be found in vugs which are holes in the rock. This vug
is formed by dissolving or eroding the parent rock and forming a deep
cavity. They are also called rock pockets and are formed from trees that
were covered by lava flow millions of years ago. It can also be found in a
geode. A geode is a hollow stone that lies buried in a parent rock that has
absolutely different mineral composition.
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