Crystals, Minerals & Rocks

What are crystals?

Crystals are solid material in which the atoms are arranged in regular geometrical patterns. The crystal shape is the external expression of the mineral’s regular internal atomic structure. Temperature, pressure, chemical conditions and the amount of space available are some of the things that affect their growth. Many crystallise from watery solutions, some from molten rock as during volcanic eruptions when lava cools rapidly.

Each mineral will always form in a range of crystal shapes. Although there are literally thousands of minerals, their crystal shape can be grouped on the basis of their symmetry into seven systems of three dimensional patterns, namely: octagonal, tetragonal, trigonal, hexagonal, orthorhombic, monoclinic and triclinic. (source: gemrock.net)

 

What are minerals?

Minerals are made of elements. Elements are simple substances that cannot be broken down into any other substance. The name of an element is written down as a combination of letters called a symbol, e.g: sodium is Na; chlorine is Cl. Salt, a combination of sodium and chlorine is thus written as a formula symbol NaCl. Many minerals are made up of large numbers of elements, so their formulas are complex. The most common minerals are those based on silicon and oxygen, Si04.

People value and search for minerals for many different reasons. Most are useful as they are the raw materials of the metals we manufacture into goods. The lead in a pencil is the mineral graphite mixed with clay. Precious metals are used in commerce and other minerals are valued as gems.

Minerals are either found in shapeless lumps which we call ‘massive’ or they can form into the special shapes we recognise as crystals. Most minerals form within the spaces between other minerals and grow into rough shapeless masses. However, if they are able to form freely in a hole or cavity in the surrounding rock the mineral takes the form of a crystal and these crystal lined cavities are called geodes, vugs or pockets. (source: gemrock.net)

 

What are rocks?

Rocks are combinations of one or more minerals that we find in nature. They can be big or small. There are three types of rocks: igneous (where you find quartz), metamorphic (where you find jadeite), sedimentary (where you find sandstones). Only a few minerals are rock forming and most rock is made from a combination of the commonest of these such as feldspars, quartz, mica, olivine, calcite, pyroxene and amphiboles. Most other minerals, of which there are over 3,000 different types, are rarely present in quantities large enough to be considered rock forming. (source: gemrock.net)

 

If you would like to know more about crystals, minerals and rocks, come and visit The Gem Museum where you will find a whole array of these samples. We look forward to welcoming you!