Solids may be crystalline: the crystal form reflects how the constituent particles pack together in a regular array. Crystals are evidence that atoms are real.
Many compounds form crystals in the solid form, as identical particles settle into a regular array, offering further evidence that atoms really exist.
When the ions in a crystal differ in size, or when water of crystallization is present, the basic unit may have a shape that dictates other crystal shapes.
A crystal's shape and system tells us the shape of the constituent units, the so-called molecules of the crystallized substance, which determines how they pack.
Crystals can form from a melt of metal or magma as it cools, from a solution as the solvent evaporates, and in a variety of biological situations.
A crystal's shape and system tells us about the relative sizes of the constituent atoms, ions and molecules that are assembled in its regular arrays.
Crystallization is a process of dynamic equilibrium, where particles are being added and subtracted from the crystal all the time at around about the same rate.
As crystals form, it is easier for particles to be removed from exposed positions than from interlinked parts of the array, so shapes are usually regular.
As a crystal forms, it is easier for new particles to be recruited to gaps in the growing array than to link to regular surfaces, so shapes are usually regular.
Igneous rocks contain crystals which formed as the hot magma cooled, allowing particles to link together in regular arrays that were able to grow in the melt.
While the elements of a crystal are laid down in regular arrays, every so often, an irregularity will creep in, producing a small flaw in the crystal structure.
The longer minerals take to form the larger and more perfect the crystals will be, as there will be more opportunities for flaws and misalignments to be undone.
Crystals form a lattice of chemical subunits arranged in a regular array, repeated on a very large scale, and this gives them their unusual shape properties.
Every crystal fits into one of the six crystal systems, all of them defined by the shapes the crystals take, determined by the way the atoms fit together.
Every crystal form has axes and planes of symmetry that define it, and this form of analysis often links two or more different shapes into a single system.
Every crystal of a substance fits the same crystal system, because the crystal is a regular array of atoms, with minor irregularities, linked by weak bonds.
When we write NaCl for sodium chloride, we indicate that the crystal contains equal numbers of sodium ions and chloride ions, and nothing more than that.
Substances which form crystals do not exist as molecules: even if we write NaCl for sodium chloride, there is no such molecule, but it is convenient to use it.
In a crystal of sodium chloride, the ions are of comparable size, and so fill the points of a cubic lattice, which results in a cubic crystal being formed.
Crystals come in specific types, determined solely by the components that make them up. Crystals have no special mystical, psychic or magical properties.
The vibrations ascribed to crystals by commercial mystics refer to the very ordinary piezoelectric effect, which is seen in a few crystals, but not all.
The only advice scientists can ever offer to crystal believers is not to eat the green ones, because they aren't ripe yet, a bit like crystal power believers.
Almost everything around you is made of crystals, including rocks, soil and all metals except mercury, so if crystals have energy or auras, so does all matter.
If a piezoelectric crystal is subjected to an alternating current at a suitable frequency, the crystal may vibrate, just as a bell vibrates when struck.
If a piezoelectric crystal is compressed, it will develop a charge across it. This is a natural property of matter, and not some mystic form of healing energy.
Crystals have an amazing healing property, but only for the sick wallets of crystal sellers, and they have also been used to resuscitate dying bank balances.
Diamonds are the hardest natural substance known, and they can only be scratched by another diamond. A few artificial compounds are harder than diamond.
Diamonds may be hard, but they are not tough, so that they may be broken, and more importantly, they have a tendency to break (cleave) in specific directions
When a crystal breaks, the fractures will mainly happen parallel to the main planes of the original crystal's surface. This is a function of its structure
Of the many minerals known to geologists, only about 120 are generally considered to be gemstones, which must have beauty, durability and rarity to qualify.
Ornamental gemstones are distinguished from other minerals simply because they have beauty due to colour (internal or reflected) and/or pattern.
Gems may be chemically similar but have different names based on colour or pattern, as in amethyst and citrine; emerald and aquamarine, ruby and sapphire.
Synthetic gemstones are made by humans and have the same physical, optical and chemical properties (within narrow limits) as the natural gems they imitate.
Liquid crystals have different properties from ordinary crystals: they can fall into crystal structures under the right conditions, or fall out of them again.