Quartz crystals can be found either individually or as aggregates of crystals, and come in various shapes such as short prismatic, elongated, needle-like forms. Their formation conditions determine their color and other properties such as piezoelectricity.

Quartz crystallography typically takes the form of trigonal-trapezohedral structures; however, over 100 crystallographic forms have been recorded for it.

Color

Quartz crystals come in an assortment of colors, shapes and patterns caused by inclusions of other minerals that alter how light passes through them. Most frequently found are light gray to milky white shades but this can also be clear, while amethyst (purple) and citrine (yellow) can also occur; smokey quartz occurs due to natural radiation exposure creating color centers within its lattice that produces its signature colors.

Chalcedony, a cryptocrystalline form of quartz, takes on different colors depending on its host mineral and any impurities within its crystal. Jasper is one variety of chalcedony with many colors and patterns; others include bloodstone, hematite, and chrysoprase as colored examples of colored chalcedony.

Certain quartz crystals feature a characteristic structure known as Brazil law twins, characterized by penetration twins which combine left- and right-handed crystal domains to produce an aesthetic pattern of straight lines and triangles on their faces.

Shape

Quartz is one of the Earth’s most abundant minerals. In its purest form, quartz resembles glass-like in appearance, while in hydrothermal ore veins and deposits it takes on various shapes and colors that vary greatly in shape and hue. Beach sand contains large quantities of quartz as well as various igneous, metamorphic, and sedimentary rocks containing it.

Quartz crystal structure is hexahedral, composed of three-fold and six-fold helical chains of SiO4 tetrahedra connected by threefold bonds that wind around a central c axis (see images below). Six of these chains can be found on every face of a hexagonal crystal.

Most quartz crystals are untwinned; however, some exhibit Japan Law Twin or Brazil Dauphine Twin features, with clockwise or counterclockwise handedness depending on which way the twin goes. Japan Law Twins tend to be flattened and often larger than untwinned crystals while Brazil Dauphine Twin domains may feature irregular shapes or pseudohexagonal habit features.

Inclusions

Quartz crystals may form with inclusions – minerals that became trapped within their host crystal as it formed – often appearing like locks of golden hair or fuzzy moss and amplifying its magical properties.

Inclusions occur during crystal growth when conditions during crystal development allow the incorporation of elements that are incompatible with its lattice at that moment in time, yet which might later separate from it when conditions change or when other minerals overgrow their host crystal host crystal. They might then eventually dislodge from it over time or can even become covered in other minerals which grow over it over time.

Quartz with inclusions has long been revered for its beauty and mystifying powers, used in various magical practices such as scrying (crystal gazing) to discover hidden truths or connect to spiritual realms. Furthermore, quartz was often chosen as gemstones, accessories and even scientific instruments throughout history.

Purity

Geological conditions and other factors often play a part in forming quartz crystal lattices with impurities due to geological processes; such impurities can be classified by size and type; common types include lattice imperfections, amorphous silica crystals and silicate inclusions (minerals or compounds). SEM-cathodoluminescence provides valuable information regarding these impurities[59].

Quartz purity is one of the key factors affecting its value and cost; untreated crystals tend to be more costly.

Ancient Greeks called quartz “krystallos and kristallos,” meaning ice crystal, due to its clear transparent appearance. Today, clear quartz is more often called rock crystal. Colored varieties of quartz are much more frequently seen and have their own specific names due to the presence of various minerals within its growth process, taking on those hues during development; such as amethyst being translucent purple while grayish-white smoky quartz comes close.