The so-called saying goes that there are thousands of types of agate and countless kinds of jade, and the same principle applies to crystals. Currently, on the market, crystals are mainly divided into pure-color crystals and inclusion crystals.
Pure-color crystals are further classified into: white crystal, citrine, amethyst, rose quartz (pink crystal), smoky quartz, green crystal, and ametrine. There are no red or blue pure-color crystals.
Amethyst can change from purple to yellow, colorless, brown, green, and other colors after heat treatment.
5.2 Rose Quartz, as defined in national standards, refers to crystals with light pink to rose red hues, commonly known in the market as pink quartz, due to the presence of trace amounts of titanium and manganese that cause coloration. There is still debate over the definition of rose quartz, with some mineralogists publishing papers advocating for the separate naming of pink quartz and rose quartz. Pink quartz, also known as Mozambique quartz in the market, and rose quartz, known as Madagascar quartz, have different characteristics. Mozambique quartz typically has transparent to semi-transparent crystals, referred to in the market as ‘jelly body’, with a cooler tone and well-developed crystal shapes, exhibiting typical crystallographic structures. Madagascar quartz is usually semi-transparent to opaque, referred to as ‘cream body’, with a warmer tone, irregular blocky occurrences, polycrystalline mineral characteristics, and a large production volume with a heavier stone quality. The terms Mozambique and Madagascar quartz, once indicative of origin, are now gradually becoming categories within pink quartz. Regardless of origin, ‘cream body’ is now called Madagascar quartz, and ‘ice clear’ pink is called Mozambique quartz. The color of rose quartz is unstable; it can fade when heated, and exposure to sunlight can lighten the color. Mozambique quartz is very sensitive to light and fades quickly under direct sunlight, while Madagascar quartz also fades but is less sensitive. When rose quartz contains needle-like rutile inclusions, star effects can be displayed with directional cutting. Pink quartz can have its color deepened through irradiation; colored wax can be used for color enhancement; pink crystal spheres are commonly filled and heat-treated. 5.3 Citrine refers to light yellow, medium to dark yellow quartz, sometimes with brown, orange, or lemon shades. The color of citrine is related to the presence of divalent iron and trivalent iron elements in its composition. Natural citrine is rare, and most citrine on the market is artificially colored. There are three methods of citrine coloring: irradiation of natural or synthetic quartz with compensation ions in cavities; heat treatment of amethyst; and heat treatment of smoky quartz. Lemon-colored citrine is referred to as ‘Donghai citrine’ in the market because most lemon yellow is derived from the heat treatment of amethyst and smoky quartz, and careful crystal enthusiasts will notice that many lemon yellows have a heavy smoky black color, even with a yellow head and black feet. Scholars have conducted experiments showing that some amethyst heat treatments can result in tea yellow, so it can only be said that the possibility of lemon yellow color change is higher, while the chance of tea yellow color change is much lower. Moreover, lemon yellow is unstable in color and easily fades when heated, while tea yellow is more stable and less likely to fade. 5.4 Smoky Quartz is light to dark brown, brown, or black crystals, also known as tea quartz or ink quartz. Smoky quartz is probably the cheapest pure color quartz; any gemstone that is dark and unattractive is relatively cheaper in price compared to other colors.Smoke quartz is produced in large quantities, with color often unevenly distributed in bands and patches. Dyed smoke quartz can turn into colorless crystal. 5.5 green quartz has a color ranging from light to medium yellow-green, with natural green quartz being extremely rare. The color generally ranges from light green to apple green. Most green quartz is a product of the process of heating amethyst to form yellow quartz. 5.6 amethyst citrine is a crystal that coexists with purple and yellow, with distinct boundaries between the purple and yellow, each occupying a part of the crystal. The bicolored crystal is due to the crystal’s twinning, with purple and yellow developing on the R face and r face of the twin crystal respectively. The main production area for amethyst citrine is Bolivia. Six, inclusion crystals: Inclusions in crystals are the ore-forming medium captured during the growth of the crystal. 6.1 Inclusion crystals are classified by color, with common inclusion colors being red-orange, yellow, green, blue, black, and white. Red-orange inclusions include hematite, garnet, rutile, limonite, and phlogopite; yellow inclusions include rutile, goethite, and pyrite; green inclusions include chlorite, actinolite, epidote, and green tourmaline; blue inclusions include azurite, lapis lazuli, tourmaline, and water silicate aluminum copper calcium stone; black inclusions include graphite, black tourmaline, and solid bitumen. White inclusions include altered chlorite, mica, healed fractures, quartz, calcite, and tremolite (Wang Ping, 2003). 6.2 Physical state classification 6.2.1 Solid inclusions are included in the crystal in the form of crystalline solid minerals or powdery, irregular substances. These substances can form before the main mineral, and their sources are mostly foreign materials formed by mechanical capture. Crystalline mineral components in quartz include mica (muscovite, biotite, phlogopite, lithium mica), rutile, tourmaline, hornblende, actinolite, tremolite, asbestos, talc, epidote, chlorite, fluorite, pyrite, graphite, hematite, and bitumen. 6.1 Hair-like crystals: Colorless transparent quartz contains needle-like, fibrous, radial, or plate-like solid inclusions such as rutile, tourmaline, actinolite, epidote, and hornblende, hence the name. The internal mineral components of golden and silver hair-like crystals in the market are rutile. Green hair-like crystals are characterized by green fibrous and fine needle-like actinolite and green needle-like, columnar epidote. Black hair-like crystals contain more black needle-like, columnar tourmaline. Blue hair-like crystals have blue needle-like, columnar inclusions, and sometimes present in a bundle-like distribution of azurite.
When the internal fibers of a hair crystal are oriented, they can form a cat’s eye effect. Hair crystals with disordered internal fibers are called ‘disordered hair’; when the fibers are arranged in three-dimensional parallel, they are called ‘aligned hair’; crystals with extremely fine silk-like interwoven mesh distribution are referred to as ‘Venus hair crystals’. Golden hair crystals contain golden-colored rutile needle inclusions within them.
When rutile is arranged in parallel plate-like formations, they are called ‘titanium crystal’ or ‘plate titanium’; when rutile inclusions combine with hematite and ilmenite to form shapes extending in six directions, they are known as ‘titanium flowers’, which are part of the Da effect of rutile inclusions within the crystal. Titanium crystal titanium flowers 6.2 Silver hair crystals contain silver-white needle-like or fibrous inclusions, typically silver-white rutile needle inclusions. Silver hair crystal 6.3 Red rabbit hair crystals contain extremely fine fluffy rutile inclusions interwoven in a mesh distribution, with the red ones called red rabbit hair and the yellow ones called yellow rabbit hair. Red rabbit hair Dyed rabbit hair Dyed rabbit hair 6.4 Copper hair crystals contain brownish-red rutile needle or plate-like inclusions. Copper aligned hair crystals often exhibit a cat’s eye effect. 6.5 Green hair crystals contain green needle-like or fibrous inclusions, usually actinolite, epidote, or green tourmaline, and are mostly dark green in color. 6.6 Black hair crystals contain black needle-like inclusions, with the inclusions typically being black tourmaline. 6.7 Blue hair crystals contain blue explosion-like inclusions, usually blue linestone. Natural blue hair crystals are very rare on the market and are one of the typical precious crystal varieties. Phantom quartz, also known as phantom crystal or spectacle crystal, refers to crystals containing some volcanic ash and other minerals. The inclusions in phantom crystals vary in color and shape. Those with green inclusions are called green phantom crystals. Similarly, due to changes in the color of the volcanic ash, red phantoms, white phantoms, and yellow phantoms are formed, and those with two or more colors are called flower phantoms or color phantoms. Based on the shape of the inclusions, they are divided into treasure pots (full pot, half pot), thousand layers, pyramids, and starry sky, among others. Green phantom Green phantom should be the most common and popular variety of phantom crystal in the market. Brazilian green phantom Zambian green phantom One-cut Zambian green phantom Red phantom Yellow phantom White phantom Flower phantom Jade phantom Phantom crystals are often subjected to dyeing, assembly, and laser internal carving treatments. Natural phantoms are often magnified to show natural mudstone inclusions with naturally dyed colors. Green phantom dyed Yellow phantom dyed Phantom colors are rigid and garish, prone to color accumulation. Strawberry quartz contains needle-like or leaf-like dark red metallic mineral inclusions, such as hematite,纤 iron ore, and magnetite, with the key point being that its matrix is quartz.The name ‘strawberry quartz’, when translated, is referred, which is both unpleasant to hear and difficult to remember, hindering its market circulation. People noticed that the internal inclusions of this crystal resemble strawberry seeds, hence it was named ‘strawberry crystal’. Later, to distinguish it from the lower-end quartzite known as ‘strawberry crystal’, it was renamed ‘golden strawberry crystal’.
Quartzite strawberry crystal is a type of quartzite jade primarily composed of macrocrystalline quartz aggregates, with minor minerals being red, star-shaped, and finely flaky, unevenly distributed manganese-iron bearing muscovite. White water body strawberry crystal contains red, star-shaped, and finely flaky, unevenly distributed manganese-iron bearing muscovite. Quartzite jade green strawberry crystal, also known as ‘Dongling stone’, and white water body green strawberry crystal, also known as ‘super seven’ in English, refers to the ‘super seven’. Super seven mainly consists of three types of crystals: purple super seven (also known as purple-red bicolor super seven or red super seven), black super seven, and golden strawberry crystal mixed together. Purple super purple crystal contains hair-like inclusions, known as ‘purple super’, and of course, you can also call it ‘purple hair crystal’, but no one basically calls it that in the market, and the same goes for black super. Fireworks super seven, as the name suggests, has inclusions that are as gorgeous as blooming fireworks. Black super (blackcurrant) red super seven fireworks super seven crystal contains extremely rich fluid inclusions, commonly appearing as gas-liquid two-phase vesicles distributed in a flocculent manner, and sometimes negative crystal-shaped inclusions can be seen. Water crystal contains larger fluid inclusions within transparent crystal, mostly gas-liquid two-phase, sometimes visible gas, liquid, and solid three-phase; these inclusions are often negative crystal-shaped or follow the shape, containing spherical or flat-round bubbles, and sometimes when shaking the crystal, the internal fluid inclusions will also move. Oi crystal is a transparent crystal containing organic matter or liquid that is insoluble in water. It is composed of some organic liquid (such as oil beads, various alkanes, etc.) and inorganic liquid. The most common oil crystal is Herkimer diamond, which is a single double-pyramid crystal produced in Herkimer County, New York, USA. It looks very similar to a diamond, and foreigners call it ‘Herkimer diamond’. The biggest feature of this crystal is that the hexagonal prism face is short with a double-pyramid structure, the crystal is transparent and shining, and it contains rich inclusions such as gas, liquid, and solid. It is called ‘Herkimer diamond’ in China. The production areas of Herkimer diamond also include Madagascar, Pakistan, Brazil, and Yunnan-Guizhou region in China. ‘A Study on the Inclusion Characteristics and Formation Environment of an Oil-Bearing Crystal’ found that the gas composition in Pakistani Herkimer diamond is methane and a small amount of ethane, the yellow liquid is alkane substances, with a small amount of aromatic hydrocarbons; the black solid inclusions are composed of asphalt.Iridescent crystals, also known as rainbow crystals. During the growth process of crystals, external forces squeeze to produce fissures. The thin layer of fissures is filled by nearby fluids again. When light passes through the thin layer to form thin film interference, iridescent colors are produced, just like a rainbow.
Colloidal flower crystals are crystals with secondary fissures inside filled with minerals such as iron oxide. Inclusions are mostly liquid phases or precipitates. When the filling is red, it is called’red colloidal flower’; when it is yellow, it is called’yellow colloidal flower’; when it is red and yellow double colors, it is called’koi colloidal flower’. Branched crystal is a crystal with secondary fissures inside filled with minerals such as manganese oxide, often presenting in dendritic or grass flower shapes. Milky crystal is a crystal with overall foggy and milky white inclusions inside. Its color is caused by fine and dispersed gas-liquid inclusions. VII. Common forms of crystals VIII. Quality evaluation of crystals