Amethyst facts – another perspective

by Nandita Ray

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.