There is no crystal like crystal

We would like to start with a short survey: what do you think of when you think of crystal?

1. A colourless variety of quartz.
2. Grandma’s chandelier.
3. “Rock Crystal”.
4. Swarowski jewelry.

Most of the answers in my circle of friends were “Grandma’s chandelier”. The catch in this poll is that all the answers are correct. So let’s get our crystal house in order, explain the main differences and finally take a look at the crystal varieties.

Although crystal is a commonly known term, most people don’t realize that there can be two fundamentally different things hidden under this term:

• Crystal as a colourless, clear variety of quartz, created by natural processes.

• Crystal as leaded glass, created by man.

First, let’s look at crystal in the sense of natural stone:

Quartz, or silica _SiO2, is one of the most abundant minerals on Earth. If quartz does not have any impurities in its chemical composition, and at the same time not even inside the crystal to color it, then it is colorless, clear quartz – rock crystal.

Due to its widespread availability, crystal is financially accessible, either in the form of mineralogical samples or cut. In the case of mineralogical specimens, quartz, and therefore crystal, consists of hexagonal prisms ending in a “canopy”, technically an arch. The surfaces of the prisms are usually horizontally grooved, which is one of the hallmarks. However, quartz/crystal can grow together in different ways, and its development can also vary, and crystal can take on different forms. At the same time, there are also synthetic crystal samples on the market, so it is, as always, worth buying from trustworthy sellers (such as us).

One of the main producers is Brazil, where the crystals can reach up to a meter long, then Russia, China, closer to our borders Austria, Switzerland. In our country, crystal was obtained from the locality of the Coral Pit in the Jeseníky Mountains for use in optics.

The crystal has a hardness on the Mohs scale of 7, so it is suitable for jewellery, however, due to its lower refractive index (it does not “sparkle” as much), you will not see much faceted crystal in jewellery. The exception is crystals that contain inclusions of other minerals. Such stones can be very attractive and you will often see them in jewellery. But more about them later in this article.

Now let us clarify the term crystal in the sense of leaded glass:

The term “crystal glass” appeared in the 17th century during the reign of Rudolf II, when cutting and polishing of various precious stones, especially crystal, was popular in Prague. Glass, which at that time was already colourless and resembled crystal in other properties, was a welcome substitute. It began to be carved and cut after the pattern of crystal products, and the term ‘crystal glass’ was coined.

Czech crystal and the art of glassmaking soon gained such fame that in the 18th century products from the Czech lands dominated the world market. Czech production at that time surpassed even the producers of the famous Venetian glass, who even tried to imitate our crystal.

Crystal glass can have different compositions, but for the production of traditional cut glass, chandeliers and jewellery, it is used with the addition of lead oxide. Leaded glass is a more pleasing material for cutters because it is both softer and stronger than ordinary glass. However, the most significant characteristic of lead crystal is its high refractive index, which makes it sparkle beautifully.

And that brings us to the famous Swarowski family company in Austria. The company produces high-lead glass, but its exact composition is a closely guarded family secret. Once cut, the stones have the unrivalled sparkle that is so characteristic of their products.

Now that we’ve explained the main differences, it can be useful to explain the other names you may encounter (and now the real fun begins):

Rock crystal.

Rock crystal is synonymous with crystal. The term was coined to distinguish natural crystal from glass, but today it is used primarily to refer to crystal of very high quality. Sometimes it can also refer to its origin, for example from alpine hydrothermal veins. And let’s not forget the marketing, the ‘mountain’ attribute simply sounds better and is more likely to attract customers.

Herkimer Diamond/Herkimer Diamond/Herkimer Crystal

A Herkimer diamond is the name for a crystal that is double-ended, i.e. the canopy is at both ends of the crystal, which is quite rare in nature. At the same time, it is characterised by the very distinctive lustre of the crystal surfaces – hence the nickname diamond.

The Herkimer diamond is the official stone of New York State and comes from Herkimer County, from which it takes its name. The area was originally inhabited by a tribe of Mohicans who called themselves “the people of the crystals” and referred to the valley in which they lived as “the place of the crystals.” The stones were very precious to them and they held them in high esteem.

Herkimer crystal jewellery is popular in the USA and is also used in engagement rings as an alternative to expensive diamonds. They are also highly valued in the field of healing. You can commonly buy a crystal with the “Herkimer” marking in our country, but it is not always a true “Herk” (as they are called in the USA). Today any double ended, very shiny crystal is sold under this name.

The Phantom

Phantom quartz or crystal refers to the phenomenon where another, less visible crystal seems to appear inside the crystal. However, it is not an actual crystal within a crystal. This “phantom” occurs during the growth of quartz. If conditions have changed and growth has stopped, other minerals may have settled on the surfaces of the crystal during this break. When growth resumed, these minerals became part of the crystal and mark its original surfaces – hence the “phantom”.

The phantom can have different colours. The most common is a green coloration when green chlorites have settled on the surfaces of the crystal, or a very fine, grayish coloration when droplets of the solution from which the quartz was formed have been trapped.

If iron minerals are deposited on the surface, the phantom will take on a red colour, while amphiboles cause the colour to turn black. Even larger mineral crystals such as garnet, fluorite or pyrite can “float” in the crystal, but again these are usually crystals deposited on the phantom surface.

And to make it not so simple, we should say that quartz, or colourless crystal, can contain various inclusions (i.e. enclosures of another substance). And according to the content of these inclusions we distinguish:

Milky quartz (milky quartz)

If the quartz is filled with inclusions of the solutions from which it was formed, or if the solutions have secondarily filled cracks in the crystal, these fluid (gas-liquid) inclusions may form various veils, tufts or filaments. The more of these inclusions there are, the more the quartz becomes cloudy, until it may be completely white and opaque. This is where the name milky quartz comes from. This type of quartz is quite common and occurs virtually everywhere. Snow-white milky quartz is often used in medicine.

Sagenite

In addition, quartz or crystal can be enclosed by inclusions of other minerals, often creating beautiful formations. Typical examples are hairpins to needles, which can be arranged in parallel or intersect completely randomly to create interesting patterns. Quartzs (crystals) with these inclusions are referred to by the term “sagenitic quartz”, short for sagenite.

Most often we can encounter inclusions of golden or reddish coloured rutile (titanium oxide) in crystal. This variety is called rutilated quartz, but at the same time rutilated quartz is also taken as a synonym for sagenite. A number of trade names can also be encountered, such as Venus hair, angel hair and Cupid’s arrows.

The main producer is Brazil, the stone is highly valued by jewellers and esoterics. Rutile can also form star-shaped needles that emerge from a cluster of hematite (iron oxide) crystals, in which case the stone is referred to as rutile star quartz or rutile star.

One can often also encounter inclusions of tourmaline in quartz or crystal. Such a stone has no proper name and is usually sold as tourmaline quartz or tourmaline crystal. The most common type of tourmaline is black tourmaline skoryl, although other varieties such as pink tourmaline rubellite may be rare. Tourmaline occurs in crystal as various stalks or needles. Sometimes tourmaline will form an amalgamation of several short needles that can form into a “sunburst” (one of the most beautiful inclusions in the opinion of the author of this article).

Strawberry quartz

Strawberry quartz, as the name suggests, is coloured pink to red due to inclusions of iron oxides (most commonly hematite, but also goethite and lepidocrocite). Although these mineral inclusions are bright red in colour due to their iron content, they may not be present in sufficient quantities in otherwise transparent quartz, and the stone may have a rather pink or sometimes orange tinge.

Medusa quartz (medusa quartz)

The terms paraíba quartz, medusa quartz and gilalite quartz describe quartz or crystal with inclusions of the rare mineral gilalite. Gilalite is a copper silicate that causes the absolutely perfect green-blue to turquoise colour of the inclusions. Copper is also responsible for the unique color of the Paraíba tourmalines, which are found in the same locality as the Medusa Quartzs, the state of Paraíba in Brazil.

Inclusions of gilalite in crystal form formations resembling the bell of a jellyfish, hence the second name.

This was an overview of the main inclusions in quartz, although it is by no means an exhaustive list.