Gemstone Summary
What are Gemstones?
Gemstones are generally minerals that have been formed over thousands or millions of years. Gemstones may be formed from pure mineral (diamond is essentially pure carbon), a simple chemical compound (quartz is silicon dioxide), or a more complex mixture of various compounds and elements (the garnet family includes a highly variable mix of iron, magnesium, aluminium and calcium silicates). The great majority of familiar gem materials are oxides or silicates (i.e they contain oxygen and perhaps silicon) and formed as crystals during the cooling of the earth’s crust over past millennia.
The physical characteristics of gemstones can be divided into:
- their hardness,
- their gravity or density,
- their colour and luster.
The hardness and gravity or density of gemstones will depend on the crystal formation of the particular gem. Gemstones may be formed in single or multiple discrete crystals (such as diamond), in massive collections of microscopic crystals and this will determine a gem’s density. Furthermore the composition of the crystals which are formed may give a variety of different shapes.
How are gemstones formed?
The basic material in gemstones is mineral. There are over 3000 different minerals on the earth, but only about 50 which are gems. These minerals are found on the earth’s surfaces and their origin dates back to the time the earth was formed.
Minerals in gemstone derive from three basic rock formations:
- igneous,
- metamorphic,
- sedimentary.
Each of these varies in the way they originate (from molten lava or the temperature at which they cooled down, or the surface on which they formed), and this in turn makes up the different characteristics and properties in gemstones.
The colour of gemstones
Colour is the most obvious feature of a gem. There are as many gems as there are colours. Intensity, tone and variety distinguishes them from one another as well as being one of the key measures of gem quality.
The colour of a gem depends largely on the way it absorbs light and this in turn is derived from their chemical composition and crystal structure.
Colour can be described as the combination of three characteristics:
- hue,
- tone,
- intensity.
Hue is the function of the frequency of light and is described by familiar terms such as red, orange, yellow, blue, green, indigo and violet. Tone is a variation from very light to very dark. Intensity is a measure of saturation, or purity of a colour. The typical human eye can identify approximately 150 pure hues, but around one million colours. The differences among colours may be immediately obvious or so subtle that direct comparison under controlled conditions is required to discern them.
At Marjo we take extreme pride in the selection of gems for our jewellery, and we undertake numerous controls and checks before a piece of jewellery reaches your hands. Each gem is individual with specific characteristics and their beauty is individual.
Leave a Comment
New to Marjo?
Access our catalogue now - it's easy!
Categories
Archives
Fair Trade
Our customers say:
Thank you for sorting out the earrings I wanted changed. It certainly helped me to keep that customer happy!
AH in MarlboroughMarjo are proud members of the British Jewellers Association
