Gemology constitutes of Gem + Logy means “the Science of Gems” which further simplified as knowledge of Gems. So “the study of chemical, physical & optical properties of gems is called Gemology.
Nature has blessed with the legacy of astonishing precious stones which includes Diamonds, Emeralds, Pearls, Yellow Sapphires, Blue Sapphires, Rubies, etc. Subject of gemology has held a high level of interest both scientifically & technologically for a long period.
To understand Gemology, it is important to make you familiar with the Mineralogy & Petrology.
Minerals
A mineral is a uniform or homogeneous substance which occurs naturally by inorganic processes in the earth has a definite chemical composition, atomic structure and physical properties. For example: Quartz, Diamond, Tanzanite etc & so on. Minerals comes under the Mineralogy a branch of Geology.
Rocks
It is mixture of minerals or the aggregate of naturally formed minerals. There are three types of rock-
a)- Igneous Rock – are the rock which originated as magma or molten rock at depth in or below the Earth’s crust. The classification of Igneous rocks are generally according to size of crystal its colour and mineral composition. These are of further two types as:
Intrusive &
Extrusive types
i)- Batholiths – In earth’s crust a large body of magma intruded which cools slowly at depth to form igneous rocks with large crystals. e.g. granite, syenite.
ii)- Dyke – Dykes is an artificial drainage channel or vertical & semi-vertical sheet of igneous rock. e.g. Dolerite is a common dyke rock. The size of dyke may comprises from few centimeter to thousand meters thick and few meters to many meter long.
iii)- Sill – It is an intrusion of igneous rock that are parallel to the enclosing layers. It is also known as threshold. Sills and Dykes exploit lines of weakness (e.g. joints, bedding planes & faults.
iv)- Lava flow – Extrusive igneous rocks are those which reach the Earth’s surface via some form of volcanic eruption. Such rocks have small crystals due to rapid cooling on the Earth’s surface. (e.g. Basalt)
b)- Sedimentary Rock – are the rock has been formed by the consolidation and the accumulation of sediment derived from pre-existing rocks. Most sedimentary rocks are characterized by parallel or discordant bedding that reflects variations in either the rate of deposition of the material or the nature of the matter that is deposited.
c)- Metamorphic Rock – The rocks which has been changed by intensive heat or pressure under the Earth’s curst. Metamorphism implies an increase in hardness and resistance to erosion. (e.g. Shale may be metamorphosed by pressure into slate; sandstone by heat into quartzite, limestone into marble etc.)
