“A crystal is a body bounded by flat faces that is an external expression of an internal order.”
From the Photographic Guide to Minerals of the World by Ole Johnsen
What Defines a Mineral?
A mineral is a naturally occurring element or chemical compound, formed as a result of a geological process, and is usually crystalline. Most minerals are chemical compounds (as opposed to containing just one element), and most are inorganic. Synthetically produced stones are not regarded as minerals, as they are produced in a laboratory, and should always be referred to as synthetic, or expressed as such in another way. There are approximately 4000 minerals known on Earth, and new minerals are being discovered all the time, so don’t expect to memorise every one of them! Most mineral names end in “ite” or “lite”, which comes from the Greek word lithos, meaning stone.
Crystalline, Amorphous or Organic?
A crystal is a homogeneous body, meaning that it has the same chemical and physical properties throughout, and is formed by a regular lattice of atoms and molecules. Crystals form geometrically, and their outer shape will ideally be limited by flat surfaces, forming flat crystal faces.
A mineral is a crystalline solid, whether or not it is limited by plane faces. Some crystals are microscopic, and not visible to the naked eye; others have a crystalline structure that does not result in plane faces, but they are still regarded as crystalline, because they possess an ordered inner structure. Some examples of this are rose quartz, aventurine and jasper. As in the case of crystals, minerals are homogeneous, and are formed through a geological process.
Amorphous minerals are not crystalline at all, but are still of geological origin and are sufficiently homogeneous to demonstrate well-defined chemical and physical properties. The reason for lack of inner structure is usually due to rapid cooling, giving them no opportunity to crystallise, for example obsidian (volcanic glass) and tektite (glass formed by a meteorite strike).
Organics are generally considered non-mineral, and have formed from living organisms. Examples are amber (compacted tree resin), pearl, coral, coal and jet. Some mineral books will list these as amorphous.
The Crystal Lattice
In most solid substances, atoms and molecules move about freely with a great deal of empty space around them. This empty space is vast, with far more space than matter, and the particles making up the atoms extremely small. If the nucleus of an atom were as large as 2 cm, the nearest electrons would be .5 km away, and no larger than a speck of dust. Because crystals have a strong electromagnetic field, and are often formed under intense pressure, their atoms and molecules are closely packed in a strict order during growth, according to the size of the molecules and how they organise themselves to produce the best fit. This creates what is known as the crystal lattice. The perfect symmetry of this internal structure will determine the outer shape of the crystal.
The Seven Crystal Systems
Crystal shapes have been divided into seven groups or systems. There are also classes within each system, but for the sake of simplicity, I will not go into them here. Each system is determined by the crystal’s axes (plural of axis), and the angles at which these axes intersect. As this involves a good knowledge of geometry, I will touch only briefly on this area of identification. Some books also look at the basic two-dimensional structure that determines the symmetry of each shape, which will also be included, as it is easier to understand and remember.
In Crystal Power Crystal Healing, Michael Gienger ascribes a different personality type to each of the crystal systems. Although I don’t work in this way, I certainly recognise subtle differences in the qualities of each system. For example, as the cube represents earth in sacred geometry, cubic crystals are generally grounding, even those we would normally link with the upper or heavenly chakras for reasons of colour.
Cubic System (also known as the isometric system)
All three axes are of equal length and intersect at right angles.
Based on a square inner structure
Crystal shapes include cube (diamond, fluorite, pyrite), octahedron (diamond, fluorite, magnetite), rhombic dodecahedron(garnet, lapis lazuli – rarely crystallises), icosi-tetrahedron (pyrite, sphalerite), and hexacisochedron (pyrite).
Common Cubic Crystals: Diamond, Fluorite, Garnet, Gold, Pyrite, Silver, Spinel
Two axes are of equal length and are in the same plane, the main axis is either longer or shorter, and all three intersect at right angles.
Based on a rectangular inner structure
Crystal shapes include four-sided prisms and pyramids, trapezohedrons and eight-sided and double pyramids.
Common Tetragonal Crystals: Anatase, Apophyllite, Chalcopyrite, Rutile, Scapolite, Scheelite, Wulfenite, Zircon
Three out of the four axes are in one plane, of the same length, and intersect each other at angles of 60?. The fourth axis is of a different length and intersects the others at right angles.
Based on a hexagonal (6-sided) inner structure
Crystal shapes include hexagonal prisms (columns) and pyramids, twelve-sided pyramids and double pyramids.
Common Hexagonal Crystals: Apatite, Aquamarine, Beryl, Cancrinite, Emerald, Goshenite, Morganite, Sugilite, Zincite
Trigonal System (Rhombohedral System)
Axes and angles in this system are similar to the Hexagonal System, and the two systems are often combined as Hexagonal. In the cross-section of the prism base of a Hexagonal crystal, there are six sides. In a Trigonal crystal there are three sides the base cross-section.
Based on a triangular inner structure
Crystal shapes include three-sided prisms or pyramids, rhombohedra, scalenohedra.
Common Trigonal Crystals: Agate, Amethyst, Aventurine, Calcite, Carnelian, Chalcedony, Chrysoprase, Cinnabar, Citrine, Dioptase, Eudialyte, Hematite, Jasper, Magnesite, Phenakite, Quartz, Rhodochrosite , Rose Quartz (rarely crystallises) , Ruby, Sapphire, Smithsonite , Smoky Quartz, Tiger’s Eye, Tourmaline
Orthorhombic System (Rhombic System)
Three axes, all of different lengths, are at right angles to each other.
Based on a rhombic (diamond-shaped) inner structure
Crystal shapes include pinacoids,rhombic prisms, pyramids and double pyramids.
Common Orthorhombic Crystals: Alexandrite, Andalusite (Chiastolite), Anhydrite, Aragonite, Baryte, Celestite, Cerussite, Chrysoberyl, Danburite, Dumortierite, Enstatite, Hemimorphite, Iolite, Peridot, Prehnite, Purpurite, Sulphur, Tanzanite, Thulite, Topaz, Variscite, Zoisite
There are three axes, each of different lengths. Two are at right angles to each other and the third is inclined.
Based on a parallelogram inner structure
Crystal forms include basal pinacoids and prisms with inclined end faces
Common Monoclinic Crystals: Azurite, Brazilianite, Charoite, Chrysocolla, Crocoite, Diopside, Epidote, Gypsum, Hiddenite, Hornblende, Howlite, Jadeite, Kunzite, Lazulite, Moonstone, Muscovite (Mica), Nephrite, Neptunite, Orthoclase, Petalite, Serpentine, Sphene, Spodumene, Staurolite, Talc, Vivianite
All three axes are of different lengths and inclined towards each other.
Based on a ‘triclinic’ inner structure, meaning ‘three inclined angles’
Crystal forms are usually paired faces
Common Triclinic Crystals: Amazonite, Amblygonite, Aventurine Feldspar, Kyanite, Labradorite, Pectolite (Larimar), Rhodonite, Turquoise, Ulexite
No crystal structure.
Common Amorphous Minerals:
Amber (organic – not a mineral), Moldavite, Obsidian, Opal
Properties of Minerals
Crystals and minerals, and particularly gemstones, are identified through several means. You may not use these these diagnostic methods, but I believe it is useful to have an idea how the properties are determined. These properties are listed in most rock and mineral books, and are helpful in recognition.
Crystal Form and Habit
A combination of the chemical composition and inner structure of a mineral will determine its properties. Many minerals are related, either because they possess the same chemical compound, or are of the same type of crystal structure. The properties of a mineral will include the outer shape, hardness, cleavage, optical qualities, type of fracture and specific gravity.
Fibrous Radiating Crystals displayed in Aurichalcite
The term habit refers to the arrangement of faces preferred by a mineral. This can also refer to its type, and can include descriptions such as long, short, fibrous, needle-shaped, prismatic, equidimensional (containing crystals of roughly equal size), columnar, tabular, or compact.
The term aggregate refers to an assemblage of crystals. An aggregate is considered to be granular if the crystals within it are equidimensional, and granular aggregates can further be described as fine, medium or course-grained, according to the size of the crystals. Aggregates are also described as scaly, hair-like, foliated, radiating, columnar, or wire-like, and also dense, massive, banded, stalactitic (formed as stalactites and stalagmites), botryoidal (shaped like a bunch of grapes), reniform(kidney-shaped), oolitic (small spheres), or pisolitic (slightly larger pea-sized spheres). In addition, some are described by the terms dendritic (moss-like appearance, although the root of the word comes from the Latin for tree), and arborescent (shaped like tree branches.) The distinction between crystal habit and shape is somewhat vague.
Hardness is gauged using a scale to determine the hardness of minerals, from one to ten, one being the softest and ten the hardest. Knowing the hardness of gemstones and minerals is of particular importance to the lapidarist or jeweller who will be working with the stone. It is also of importance in recognition, but for crystal healers, it is beneficial to know hardness in order to take proper care of the minerals you are working with. If a stone is soft, it will be easy to scratch, and therefore should not be carried unprotected with other stones.
The term hardness refers first to scratch hardness, and then to cutting resistance.
Scratch Hardness Scratch hardness is the resistance of a mineral when scratched with a pointed testing object. The Viennese mineralogist, Fredrich Moh (1773-1839) set up a comparison scale using ten minerals exhibiting different degrees of hardness. This scale is still in use today, and is known as Moh’s Hardness Scale. Gemstones of the hardness 1-2 are considered soft, 3-5 medium hard, and those over 6 hard (formerly this was 8-10, but has since been changed to incorporate other commonly used gemstones). Those gemstones graded below 7 can be scratched with dust, which may contain particles of quartz, and these stones should be carefully handled to avoid scratching and the resulting dullness of lustre.
Cutting Resistance This is of more importance to the gemstone cutter. In some stones, the hardness varies according to the direction of the cut. For example, the hardness of kyanite along the length of the crystal is 4 – 4.5, but when cutting across the crystal, the hardness is 6 – 7.
Mineral Used for Comparison
Simple Hardness Tester
Can be scratched with fingernail
Can be scratched with fingernail
Can be scratched with copper coin
Easily scratched with knife
Can be scratched with knife
Can be scratched with steel knife
Scratches window glass
Cleavage and Fracture
Rose Quartz displaying Conchoidal Fracture
Many gemstones can be split along flat planes, known as cleavage planes. This is related to the lattice of the crystal (see the section on Crystal Systems). Cleavage refers to the ease with which a crystal can be cleaved, or split along a flat plane. If you’ve ever knocked your favourite fluorite pendant or ornament, and found it has broken along a straight line, you have witnessed cleavage. Most fluorite octahedrons are intentionally created in this way. Cleavage is usually listed in three categories: perfect (fluorite), good (sphene) and imperfect (peridot). Knowledge of cleavage is important for lapidarists, as the rise in temperature through soldering can create fissures along the cleavage planes, leaving the stone weak and easily broken. When faceting a stone with perfect cleavage, the facets must be transverse to the natural cleavage lines, or again the stone will be weakened and vulnerable. Cleavage is used to divide and break off faulty areas of large gemstones, although these days a saw is more frequently used.
Fracture refers to the breaking of a stone with a blow, causing irregular surfaces, and the way in which these surfaces present can sometimes be used to identify a mineral. The categories for fracture are: conchoidal (or shell-like), uneven, smooth, fibrous, splintery or grainy. An example of fracture for identification is quartz and some other high-silica content minerals, which have a conchoidal fracture. Stone Age tools utilise quartz minerals or obsidian. The napping, or chipping away of material to create a sharp edge, demonstrates conchoidal fracture. Other categories are fairly self-explanatory.
Density and Specific Gravity
In the past, the specific gravity of a mineral was measured by the ratio of its weight to the weight of the same volume of water. This has been replaced by density, usually expressed as grams per cubic centimetre (g/cm2). There are two methods of measuring the density of minerals: Hydrostatic Balance, using the buoyancy principal, and the Suspension Method, using a series of standardised heavy liquids (very expensive and potentially dangerous due to the toxicity of the heavy liquids). There are instructions for creating your own Hydrostatic Balance in Gemstones of the World by Walter Schumann, should you be interested.
Colour of Streak
Because one variety of crystal may occur in many different colours, caused by impurities, colour itself is not considered to be diagnostic. Streak is determined by “streaking” the mineral on a rough porcelain plate. The streak left will be the inherent colour of the mineral, which is constant.
Refraction occurs when a ray of light leaves one medium, such as air, and enters another, such as water or a crystal, and the interface between these two media. The effect is that of bending the light, such as when a stick is partially immersed in water. The amount of refraction in crystals is constant, and can be used in identification. A good example of double refraction is optical calcite, in which half the incident light travels straight through the crystal, while the other half of the light is bent. If you place the crystal over a printed piece of paper, the image or writing will appear double.
Dispersion occurs when a colourless crystal disperses white light into its spectral colours, in the way that a prism does. This is especially notable in diamonds, and referred to as “fire”.
Colour is one of the most important tools in identification, but it is not diagnostic, as numerous crystals are the same colour as others, and many also come in a wide range of different colours. Listing crystals according to colour, as some crystal healing books are prone to do, is not an efficient means of identification.
The Absorption Spectrum refers to the spectral colours of light as they emerge from a gemstone. Certain wavelengths, or colour bands, are absorbed, and the colour of the gem is formed from a mixture of the remaining parts of the original white light.
The two main causes of colouration in minerals are absorption of parts of the incident light, which affects the wavelengths of light leaving the mineral, and the refraction and scattering of light. When white light passes through a mineral, and none of the colour spectrum is absorbed, that mineral will appear to be colourless or white. If the entire colour spectrum is absorbed, the mineral will appear grey to black. If only certain wavelengths of colour are absorbed, the colour displayed by the mineral will be those wavelengths that pass through it. The wavelengths of light that are absorbed represent energy that has been expended moving electrons from one energy level to another, and the specific wavelengths required to do this will vary not only between different elements, but are also determined by the electron configuration of a particular element. When there is a transition of electrons from one level to another, this can cause a change of the wavelengths absorbed, even when the element is the same. An example of this is azurite and malachite, both of which are hydrous copper sulphates, but azurite is blue while malachite is green.
As you can see, the absorption of light is very complicated, and we will not go too deeply into it here. If you are interested in studying this further, more information can be found in Photographic Guide to Minerals of the World by Ole Johnsen (OUP), and Gemstones of the World by Walter Schumann (see Bibliography for details).
A simpler way of observing causes of colouration is to look at the colour range created by certain elements. Some minerals receive their colouration from the inclusion of impurities when the crystal is forming. In these cases the impurities are not included in the chemical formula, as they are not considered part of the actual make-up of the mineral. For example, all quartzes have the chemical formula SiO2 (silicon dioxide) whatever included elements are present, so clear quartz, amethyst, citrine, and even tiger’s eye and aventurine will be the same chemical formula. In other cases, the colour-causing element will be part of the chemical make-up, and therefore obvious in the chemical formula. It is important as a crystal healer to understand the chemical reasons for colouration, as this will have an effect on the vibrational qualities of the mineral. In crystal healing we use both colouration (as in Colour Therapy), as well as the vibrational qualities of the elements contained in the mineral.
Here are some of the most common colourations due to the presence of certain elements:
Aluminium: Blue, green (and grey) Examples: Kyanite, variscite; small traces in smoky quartz will result in light absorption when exposed to gamma radiation or x-ray. Chlorite: Green Examples: Bloodstone (colouration can also be from included hornblende), and in some green-coloured quartz phantoms Cobalt: Pink, silver Examples: Cobaltocalcite; cobaltite Copper: The most common cause of green, turquoise and some blue colouration in minerals. Examples: Malachite, turquoise, dioptase, chrysocolla, azurite Chromium: Pink to red; also green Examples: Ruby; also emerald, jade, moss agate (which can also include hornblende), fuchsite mica, chromium diopside; alexandrite is between the two absorption spectra, and will appear red in artificial light, green in daylight. Iron and Iron Oxide: Blue to violet; yellow, orange and red; metallic silver to pewter Examples: Amethyst, iolite, blue tiger’s eye, blue and yellow sapphire (blue sapphire also contains titanium), aquamarine; also citrine (due to heat and possibly gamma radiation); red jasper, gold tiger’s eye, carnelian, tangerine quartz, red jasper; also responsible for the pinkish tint on lemurian quartz and the red speckles in harlequin and strawberry quartz; hematite, magnetite (lodestone), goethite Lithium: Lavender to purple, mauve Examples: Lithium quartz, lepidolite, sugilite Manganese: Pink Examples: Rhodonite, Rhodochrosite, Mangano calcite Nickel: Green Examples: Chrysoprase, Variscite Titanium: Pink, purple – blue Examples: Rose quartz, sapphire (also contains iron)
Transparency Transparency or clarity of a gemstone is a factor in grading and evaluating. Transparency will be affected by the inclusion of impurities, or fissures within the crystal. The fewer impurities or flaws, the greater the transparency.
Lustre The characteristic lustre of many gemstones is used to help classify the stone, whether the stone is cut and polished, or a natural specimen. Lustre is not measurable, and is described with known objects, differentiated as metallic, diamond, greasy, pearly, silky, waxy, resinous and vitreous.
Pleochroism Some minerals will display a different colour or depth of colour when observed at different angles, due to the differing absorption of light in double-refracting crystals. A classic example of pleochroism is Alexandrite, which appears green in natural daylight, and red in incandescent light, due to differences in light frequency and absorption.
Light and Colour Effects This sub-section refers to light or colour effects that do not relate to a gemstone’s body colour, and are not caused by included impurities.
Adularescence: The play of light associated with moonstone (a feldspar), as a result of interference phenomena of the layered structure of the crystal. Asterism (from the Latin aster, meaning star): The six-pointed star effect displayed in minerals such as sapphire, ruby and rose quartz, when cut in a sphere or cabochon. This is usually caused by light reflecting off fibrous inclusions in the crystal, such as rutile.
Aventurescence: The colourful and glittering play of light displayed in different types of aventurine, caused by small plate-like or leaf-like inclusions. The inclusions are hematite or goethite in aventurine feldspar, and hematite or fuchsite (mica) in aventurine quartz, the latter of which is the one most commonly called aventurine. Chatoyancy (from the French chat, or cat): Chatoyancy is also known as “cat’s eye effect”, and refers to a single line of light reflected from parallel needles, fibres or channels within the crystal. The most valuable cat’s eye occurs in chrysoberyl, but the effect also occurs in quartz and both blue and gold tiger’s eye..
Labradorescence: Labradorescence is the metallic iridescent play of light that is usually observed in labradorite, hence the name. It is also known as schiller. The cause is not completely understood, but is probably due to lattice distortions combined with microscopic inclusion of other minerals. Orient: The iridescence in pearls. Play-of-Colour: The flash of rainbow colours that occurs in opal, caused by microscopic spheres of the mineral crystobalite included in a silica gel within the gemstone. Luminescence: Luminescence is the emission of visible light under the influence of specific light rays, most commonly ultraviolet, the effect of which is referred to as fluorescence. Fluorescence is not diagnostic, as specimens of the same gemstone will fluoresce in completely different colours, or not at all.
Chemical Composition of Minerals
The purpose of the section is to introduce you to the elements that make up minerals commonly used in crystal healing, and also to think about the implications of these elements in healing.
I encourage you to visit the Web Elements site (www.webelements.com), which has wonderful online version with lots of interactive material, including the uses of each element in both industry and biology. There is another online Periodic Table that interacts with Wikipedia entries on each element: http://www.ptable.com.
Chemical composition of minerals is shown by a chemical formula. Impurities are often responsible for colouration, but these are usually not reflected in the chemical formula.
To understand the importance of knowing the chemical make-up of minerals, let’s look at a few examples. You will find by looking at the periodic table that calcite (CaCO2) is a calcium carbonate. With basic knowledge of anatomy and physiology, you will know that calcium is the main constituent of the skeletal system, and therefore calcite is often used in crystal healing to help mend fractures of bones or treat bone density issues in post-menopausal women. Hematite (Fe2O3) is an iron oxide. Iron helps to maintain healthy red corpuscles and oxygenate the blood, and hematite is frequently used to treat anaemia as well as circulatory problems, as well as traditionally being employed to staunch blood flow in wounds.
The best way to familiarise yourself with chemical composition is to go through the Periodic Table, and look up the uses of the different elements, but some of the most common are listed below, along with their biological role in the human body:
Aluminium may be involved in the action of certain enzymes, but aluminium compounds are toxic, and it has been linked with Alzheimer’s disease
No biological role, but small doses are believed by some to stimulate the metabolism
Although toxic, as an ultra-trace element it is essential in humans, and its lack results in inhibited growth
Barium has no biological role, and is highly toxic, although it is employed in internal body imaging; it is used in glassmaking, rubber making and for creating green colour in fireworks and pyrotechnics
1.5% of total body mass in humans
Forms part of the cell walls and bones; the ionized form (Ca2+) is necessary in blood clotting, release of hormones, contraction of muscle, and other processes
18.5% of total body mass in humans
Essential to life, as it forms the backbone chains and rings of all organic molecules
0.2% of total body mass in humans
The anion (negatively charged particle) is the most plentiful anion in extracellular fluid, and is essential in maintaining fluid balance in the body
Trace chromium is involved in glucose metabolism; any more than trace is toxic
The core of vitamin B12, essential in absorption of iron
Essential to all life as a trace element; the key component of redox enzymes and of haemocyanin; a good conductor of both heat and electricity, and thought by many to act as an anti-inflammatory and to aid pain relief when worn, by drawing off the inflammation; copper has bacteriostatic qualities, and malachite, a copper ore, has been used for thousands of years in the treatment of infection
Fluorine (as fluoride, in an organic form) is added to drinking water in order to render teeth impervious to bacterial attack
Gold has no biological role, but is used in some drug treatments for rheumatoid arthritis
3.2% of total body mass in humans
A constituent of water, and in most organic molecules
0.1% of total body mass in humans
Essential for carrying oxygen around the blood stream
Toxic, affects the nervous system and gut, but is also used to block x-rays, and can be useful for certain types of protection and blocking of electromagnetic stress
Lithium-based compounds, such as lithium carbonate, are used to treat manic-depressive (bipolar) disorders.
Essential for the action of some enzymes; deficiencies can lead to infertility and malformation in growth
Essential for all life, and plays a role in nitrogen fixation (a process by which the normally unreactive nitrogen gas is turned into other compounds) enzymes, and nitrate reduction enzymes. Too much molybdenum can block iron absorption.
An important trace element, thought to be necessary for the health of the liver
65.0% of total body mass in humans
Essential to life and a component of water; used to generate ATP (a molecule used by cells to temporarily store chemical energy)
Potassium salts are essential for both animals and plants: the potassium cation (positively charged particle: K+) is the major cation in intracellular fluids, and is necessary for nerve and muscle impulses; potassium is essential for nerve and heart function.
Necessary to rats and chicks (and one would assume humans…) for skeletal development; also used for making glass, transmitting energy (for example in computer chips), and has excellent optical properties
Silver has no biological role, but is often used for cleansing; colloidal silver is taken internally, and plasters are sometimes lined with silver, because of its antibacterial properties.
.2% of total body mass in humans
Important for regulation of fluids in animals and humans; the main extracellular cation, necessary for nerve and muscle impulses; used in cleansing
No biological uses, but oddly is used for the red colour in fireworks (strontium is the main constituent of celestite, which is blue-grey)
No biological uses, but incredibly strong, light weight, flexible, resistant to corrosion, non-magnetic, and, when used in pigment; reflects infrared radiation; a main component in joint replacement, especially ball-and-socket joints, due to its strength and light weight, and in dental implants, as it easily fuses with bone tissue
Vanadium is a trace element, and it is not known in what way it is biologically important for humans, but according to the WebElements website, is an essential nutrient for rats and chicks, apparently.
A key component to many enzymes; contained in insulin; plays a role in reproduction, sexual maturation, male sexuality, and the immune system
The periodic “law” of chemistry recognises that properties of the chemical elements are periodic functions of their atomic number (that is, the number of protons within the element’s atomic nucleus). The periodic table is an arrangement of the chemical elements ordered by atomic number in columns (groups) and rows (periods) presented so as to emphasize their periodic properties.
There are many different ways, sometimes ingenious, of arranging the chemical elements according to which properties are of particular interest but that shown here is a standard form of the periodic table. The relative merits of various other periodic table organisations is still the subject of debate.
While the name Dmitri Mendeleev is usually credited with the with the form of periodic table as we know it today, many other excellent researchers made profound contributions to its development, including Antoine Lavoisier, Jöns Jakob Berzelius, Johann Döbereiner, John Newlands, Alexandre-Émile Béguyer de Chancourtois, Lothar Meyer, and others.