Quartz crystals range in both color and size, while also showing various other traits such as asterism, coontail and growth zoning.

Asterism is an optical effect in which crystals rotate the plane of polarization of light passing through them, creating an optical effect which can be observed under bright lighting conditions.

Color

Quartz crystals, composed of silicon dioxide, come in an assortment of colors and shapes due to impurities forming within the stone as it forms, altering its chemical structure to produce different hues and shades.

Pure rock crystal is colorless; however, impurities in its composition give rise to distinct shades such as milky quartz (with many inclusions), amethyst (from iron impurities), citrine (due to aluminum or radiation exposure) or other variations within natural quartz stones.

Green quartz, or prasiolite, promotes relaxation and creativity while stimulating geode collectors. Rare blue inclusions of ajoite are prized among collectors; double-terminated quartz from Keokuk, Iowa is particularly prized due to its distinctive blue tint with inclusions of rutile, hematite and other minerals; these unusual inclusions indicate genuine geodes and can often be identified by features like Airy’s spiral or zebra stripes – two distinctive hallmarks of real crystal.

Size

Quartz crystals can grow to immense sizes; well-cut transparent specimens may weigh several pounds. Although hard, quartz scores 7 on Mohs’ scale of mineral hardness. Unfortunately, it’s also very brittle, easily fractured or chipped.

Quartz crystal oscillators are widely used timekeeping devices such as wristwatches and clocks because of their precise vibratory patterns, making quartz an excellent material to utilize as timekeepers. Furthermore, the piezoelectric effect in quartz produces electric voltage when pressure is applied along certain directions within its crystal.

Electronic device quartz tends to be of extremely high quality, grown on seed crystals selected specifically for their superior qualities. Due to shortages during World War II, large-scale production began using hydrothermal techniques in laboratory settings. Today’s majority production is synthetic. While natural quartz tends to feel cooler to the touch than its synthetic counterparts and has inclusions and patterns not replicated by synthetic crystals, synthetic production often produces identical crystals with more pleasing aesthetic qualities than its genuine counterparts.

Shape

Minerals’ crystalline structures give them their distinctive shapes. Crystals may form squares, rectangles, triangles, diamonds and hexagons; quartz crystals usually have long pointed forms but cubes can also form; when covered by bands of dark brown-coloured chalcedony, known as sardonyx, its colour ranges from opaque to transparent.

This smoky quartz features fadens (ribbed surfaces) that indicate it was interrupted in its growth at some point, possibly as a result of an accumulation of foreign minerals such as chlorite which inhibit growth by attaching itself to its surfaces and blocking growth.

This faden quartz features three dents likely formed by mechanical stress caused by tectonic activity at Erongo Mountains and Klein Spitzkoppe mountains in Namibia. These three dents create a pattern similar to garden lattice fencing; this type of intergrown double terminated quartz is known in German as Gitterquarz.

Origin

Quartz crystals can be found in numerous geological settings. They form when silicon and oxygen atoms from magma combine with each other to form a crystal framework – this gives quartz its hardiness, unique transparency, and piezoelectric properties that set it apart from other minerals.

Quartz’s crystalline structure renders it extremely resistant to chemical and physical weathering, explaining its prevalence in beach sand. Furthermore, quartz is the most abundant mineral on Earth’s crust and second most prevalent mineral in space.

Quartz comes in many varieties, each distinguished by different hues and inclusions. Some types, like rose quartz and amethyst, have long been considered semiprecious gemstones since antiquity; other varieties such as aventurine and sardonyx are used for carving figures like cameo gems. Quartz can even generate electricity when subjected to mechanical pressure – an effect known as piezoelectricity, first noted by pre-Marie Curie French scientist in 1880.