Crystals Rocks Minerals | Understanding the Difference
What Exactly are Crystals Rocks and Minerals?
Crystals rocks and minerals are the building blocks of our planet and mankind has had an inherent attraction to them since the dawn of time. Their use for personal adornment can be traced back at least 82,000 years and throughout history they have remained a constant source of intrigue and fascination. They have been used as tools, been carried as talismans, have been carved into luxury objects and have long been associated with status, wealth and power. The belief that rocks and minerals hold magical and medicinal powers as well as healing properties dates back thousands of years and the stories and myths associated with these inanimate objects have been passed down from one generation to the next. In today's society the practice of using crystals to promote health and well being is widely known as crystal healing and despite it being considered by some to be a pseudoscience, it remains hugely popular and is a multi billion dollar industry.
The lure of crystals rocks and minerals is universal and common to almost every human being on the planet yet few people can really explain exactly what they are or how they came into existence. We're all familiar with the words rocks, minerals, crystals and gemstones but each term represents something slightly different. Whilst rock tends to be used to describe any geological related material that's hard hence the phrase hard as a rock, it actually describes a material that's made up of more than one mineral. Minerals on the other hand are naturally occurring substances made up of crystals which in turn are made up of atoms. The term crystals is also widely used to describe tumbled stones which are small rounded shaped fragments of polished rocks and minerals that have been formed in a rock tumbler. Lapis lazuli is often described as a mineral which is incorrect because it's made up of several different minerals so is in fact a rock yet when tumbled it's often referred to as a crystal. No wonder there's so much confusion surrounding the difference between crystals rocks and minerals.
The study of crystals is known as crystallography, the study of rocks is petrology, minerals is mineralogy and gemstones is gemmology. Geology is the study of the earth, its history, the rocks of which it's constructed, their structure, where they came from, how they have changed over time and how they continue to change. Whilst all of these subjects overlap to some degree they are grouped together under the larger heading of "science".
Definition of a Gemstone
When a piece of a rock or mineral is cut and polished (often but not always) to be used in an item of jewellery, it becomes known as a gemstone. Having said that if you cut and polish a piece of granite it doesn't automatically deserve the right to be called a gemstone, well not officially. For a stone to be classified as a gemstone it must include certain attributes some of which include colour, durability, beauty and rarity. Beauty and rarity for most people rank as the two most important factors. Durability encompasses hardness, toughness and stability.
Definition of a Crystal
A crystal is a solid that's made up of a microscopic highly ordered arrangement of atoms that form a repeating three dimensional pattern known as a crystal lattice. A typical crystal contains billions of atoms and the shape they form is known as the crystal structure whilst their formation and subsequent growth is called crystallization. The crystal structure for each type of mineral is always the same and should it change the result will be a different mineral. Pyrite and marcasite both have an identical chemical make up in that they’re iron sulphide (iron and sulphur) minerals but the one you end up with depends on the formation of the atoms or the crystal structure that's present. Another example is calcite which has more crystal structures than any other mineral, its chemical make-up is identical to aragonite yet they're two different minerals. A crystalline structure serves as a tool of identification because it's unique and specific to each mineral variety. The crystal structure in a quartz crystal for example will always be exactly the same.
Repeating arrangement of atoms in a crystalline solid
Crystals are present in many solids but because of their size which can sometimes make them difficult see and the fact that they're tightly interlocked, people rarely take much notice of them. Many crystals are so minute they can only be seen through a powerful microscope whilst others are large enough to be seen with the naked eye. An amethyst geode whose crystals are clearly visible is likely to attract far more attention than a mineral whose crystals may not be so easy to see. The long terminated points often present in quartz are an example of large crystals and their external shape like the shape of all crystals, is defined by the crystal structure or shape of the repeating arrangement of atoms inside. Crystals that can only be seen with the aid of powerful magnification are known as cryptocrystalline but microcrystalline is also used and specifically means they're microscopic. Macrocrystalline means crystals are visible to the naked eye.
The substances which most of us are familiar with exist as a gas, liquid or solid and all three are made up of atoms but the specific arrangement is different for each. In a solid that's crystalline or made up of crystals, the atoms form a three dimensional highly ordered repeating pattern but when the pattern is disjointed or random the solid becomes known as amorphous or non crystalline. The word amorphous comes from Greek and means without a definitive shape or form. Examples of amorphous solids include obsidian which is natural volcanic glass and man-made glass which is produced by heating sand which is silicon dioxide otherwise known as quartz. Non crystalline solids occur when a liquid cools so fast that crystals didn't have time to grow.
In the diagram below the solid on the left exhibits atoms in a highly ordered repeating arrangement which makes it crystalline (mineral) but those on the right have no order or structure which makes it amorphous or non crystalline. Mineraloids and glass are both amorphous solids.
Crystals form when a liquid cools and solidifies and whilst some grow very quickly, others can take thousands of years or even longer. The slower the cooling process the larger the crystals. A snowflake can be one single crystal or a collection of many. Impurities within a crystal can affect all stages of the crystallization process and are often responsible for a change in colour although colour change can also be caused by heat. A crystal may be exposed to heat naturally during its formation or at some point later in its life cycle. Rocks and minerals have been heated by man for thousands of years in order to enhance or change their colour and most of the world's finest gemstones have been heated. The purple colour seen in the mineral amethyst is the result of impurities of iron whilst the yellow colour of citrine is often produced by heating amethyst because natural citrine is quite rare.
The word "crystals" is often used as a general term to refer to rocks and minerals used for the purpose of crystal healing. It should be remembered however that not all of these naturally occurring solids will have a crystalline structure so they're not crystals in the true sense of the word.
Definition of a Rock
Rocks tend to be made up of at least two different minerals although some are made up of just one. The minerals which bond together to form a rock are all relatively common and are referred to as rock forming minerals. Granite which one of the most common types of rock is made up of the minerals quartz, mica and feldspar. Marble which is limestone that's been through the process of metamorphism is an example of a rock that's made up of just one mineral being calcite and another is quartzite which is consists primarily of minute grains of quartz. With rocks being made up minerals as opposed to crystals they do not have a crystal structure.
Rock types are divided up into three main groups which are sedimentary, igneous and metamorphic and all three were formed through different geological processes. One way to explain the nature of a rock is to think of it as a solid mass made up of individual grains all of which have been compacted together and each grain is a separate mineral. In rocks that are made up of more than one mineral the nature of the grains and the way in which they come together defines its ultimate hardness. Rough grains which fit tightly together restrict the amount of room that's left available for moisture hence the rock will be hard and non porous. Finer grains are likely to have a more rounded shape hence won't lock together as tightly which leaves room for moisture and air so the rock ends up being softer and is more likely to be porous.
Igneous rocks are the result of magma or lava which has cooled and solidified. Sedimentary rocks are made up of layers of sediment which have accumulated under water, over time the mass becomes compacted and is eventually cemented together but the process can take millions of years. An existing rock which undergoes a profound transformation caused by heat or pressure is known as a metamorphic rock. During the process of metamorphism the specific arrangement of minerals is altered and their individual crystal structure may also change.
Definition of a Mineral
A mineral is made up of naturally occurring inorganic solids which means they're void of any living matter but to correctly be described as a mineral a substance must also be crystalline. Some minerals have the ability to crystallize in more than one way and a different crystal structure will create a different mineral.
Not all mineral-like substances are crystalline, those which lack any significant crystal structure are known as a mineraloid. The most common mineraloids include amber which is tree resin, jet which is a compact form of coal that comes from plant matter, pearl which is formed by shelled molluscs, obsidian, shungite, opal, coral and shell both of which are the secreted skeletons of marine creatures.
Most minerals are chemical compounds which means they're made up of two or more chemical elements, an example is quartz which is made up of one atom of silicon and two of oxygen. A chemical element is a substance which contains just one type of atom, minerals made up of a single element are known as native elements and include copper, carbon (diamond is a solid form of carbon), gold, titanium and silver. Other chemical elements include manganese, sodium and hydrogen which is the lightest of all elements and formed some fourteen billion years ago soon after the big bang along with trace amounts of beryllium. Although an element may be a liquid, solid or gas, bromine and mercury are the only two liquids.
The number of minerals known to man varies from 2,722 to 6,500 depending on the reference that you read. Approximately 150 new varieties are discovered around the world each year.