An Introduction to Simulants or Imitation Gem Materials

Glass and plastic imitation chalcedony

The jewellery industry uses special terms for manufactured and look-alike gemstones: synthetic and simulant. The differences between them are subtle, but very important. Synthetic refers to a man-made material with essentially the same chemical composition, crystal structure, and optical and physical properties as the natural gem material. There are also materials that simply look like natural gems. These products are called simulants or imitations, and can be either natural or man-made. Substitute is an older term for the same thing.

Man-made simulants

Synthetic spinel – synthetic spinel is often used as a simulant because it can mimic the look of many different natural gems (such as sapphire, zircon, aquamarine and peridot), depending on its colour. Its accurate reproduction of a wide variety of colours makes it a common choice for imitation birthstone jewellery. Prevalence: common.

  Synthetic Spinel
This group of synthetic spinel boules and cut stones illustrates how this man-made material can be made to look like other gemstones, such as ruby and various colours of sapphires.

Synthetic rutile – synthetic rutile was introduced in the late 1940s and used as an early diamond simulant. Made by the flame-fusion method, it is nearly colourless with a slight yellowish tint, but it can be made in a variety of colours by doping (adding chemicals during the growth process). Prevalence: rare. 

  Natural Diamond and Synthetic Rutile
Natural diamond (left) and various diamond simulants: (inner left to right) synthetic rutile, gadolinium gallium garnet (or GGG), synthetic spinel, strontium titanate, synthetic corundum, yittrium aluminium garnet (or YAG), and colourless zircon.

Strontium titanate – this colourless manmade material became a popular diamond simulant in the 1950s. However, its dispersion (the optical property that creates fire in a faceted gemstone) is over four times greater than diamond. Strontium titanate is most often produced by the flame-fusion method and can be made in colours, such as dark red and brown, by adding certain chemicals during the growth process. Prevalence: rare.

YAG and GGG – several manmade materials have been used as diamond simulants over the years. In the 1960s, yttrium aluminium garnet (YAG) and its “cousin” gadolinium gallium garnet (GGG) joined classic simulants like glass, natural zircon and colourless synthetic spinel. YAG and GGG are also available in a variety of colours. Prevalence: rare. 

Yittrium aluminium garnet (or YAG) can be manufactured in a variety of colours such as those seen here. The colourless crystal is used as uncut material to fashion diamond simulants.

Synthetic cubic zirconia (CZ) – early diamond simulants have been almost entirely replaced in the past three decades by colourless CZ. It is made by a process called skull melting. As the material melts, the outer portion is kept cool to form a solid crust which then contains the melt. CZ can be produced in almost any colour, and in darker hues it is a convincing alternative for gems in purples, greens and other dark tones including black. Prevalence: common.

  Synthetic Cubic Zirconia
Cubic zirconia (or CZ) is also manufactured in a variety of colours, though colourless CZ makes the most convincing colourless diamond simulant.

Synthetic moissanite – colourless synthetic moissanite was introduced in the late 1990s as a diamond simulant. It is closer to diamond in overall appearance than any previous diamond imitation, but now it is most often sold as a gem in its own right. Prevalence: occasional.

  Natural diamond and synthetic moissanite
Natural diamond (left), and (inner left to right) laboratory grown moissanite in the near colourless to greenish range.

Glass – manufactured glass is an age-old gem imitation that is still used today. Since glass can be manufactured in virtually any colour, this makes it a popular substitute for many gems. Although it is less brilliant, glass is used to imitate stones like amethyst, aquamarine and peridot. It can also be made to look like natural phenomenal gems, like tiger’s eye and opal, and fused layers of glass can imitate the look of agate, malachite or tortoise shell. Prevalence: common. 

  Glass Malachite and Rutilated Quartz
Glass, such as this material, can be made to look like a variety of gemstones; in this case glass makes a convincing substitute for malachite (left) and rutilated quartz (right).
  Opal Simulants, slocum stones
A glass material known as “slocum stone” can mimic the appearance of opal.

Plastic – plastic is often used to imitate gemstones in inexpensive fashion jewellery. However, this modern man-made substance has also been manipulated into convincing imitations of organic gems like amber, pearl and coral, or aggregate materials like jade, turquoise and lapis. Plastic is not a durable imitation, so special care must be taken to prevent damage. Prevalence: common.

Quench crackled quartz – Natural colourless quartz can sometimes be subjected to thermal shock, known as “quench crackling”. The colourless material is first heated, and then subjected to quenching in a cold, liquid solution — such as water. The sudden contraction causes the material to develop a series of cracks that radiate throughout. Because these are surface-reaching fractures, the quartz can then be subjected to additional immersion in a dye solution, allowing the fractures to be filled with coloured liquid. This makes a convincing simulant for natural gems such as emerald, ruby and sapphire, although the fractured and dyed appearance can quickly be seen under the microscope. Prevalence: occasional. 

  Quench Crackled Quartz
Colourless quartz can be subjected to thermal shock that creates a series of tiny fractures throughout the stone. Dye is then introduced, causing the material to simulate many different kinds of gems, in this case—emerald and ruby.

Ceramic beads – you’ve probably heard the term “ceramic” applied to clay pottery. In general, a ceramic can be any product made from a non-metallic material by firing at high temperature. Two popular non-faceted gems, imitation turquoise and imitation lapis lazuli, are produced by ceramic processes. During this process, a finely ground powder is heated and sometimes placed under pressure to recrystallise and harden to produce a fine-grained solid material. Prevalence: occasional.

Imitation turquoise – the cool blues and greens of turquoise have attracted people for centuries. More than 5,000 years ago, Egyptian pharaohs first adorned themselves with turquoise. The familiar gem is a microcrystalline aggregate that often features attractive, vein-like inclusions of host rock known as matrix. In the early 1970s, Gilson introduced an imitation turquoise as well as an imitation lapis. Prevalence: occasional. 

  Gilson Imitation Turquoise and Lapis Lazuli
Gilson imitation turquoise and lapis lazuli make convincing substitutes for their counterparts found in nature.

Imitation lapis lazuli – dark blue lapis, treasured by ancient civilisations, has been mined in Afghanistan for more than 6,000 years. The gem is an aggregate of several different minerals. It sometimes contains gold-coloured flecks of pyrite that can enhance its appeal. Gilson’s lapis is more accurately considered an imitation because it has some ingredients and physical properties that are different from natural lapis. Prevalence: rare. 

Assembled Stones:

When manufacturers glue or fuse two or more separate pieces of material together in the form of a faceted gemstone, the result is called an assembled or composite stone. The separate pieces can be natural or man-made. The flat surfaces that are glued together are parallel to the large table facet of the gem so as to impart a more uniform face-up colour.

Doublet – a doublet consists of two joined segments. Prevalence: common.

A doublet, such as this one, contains two joined portions of a gem that are held together by colourless glue, as a profile view of this material shows.

Triplet – a triplet has three segments, or two segments separated by a layer of coloured cement. Prevalence: common.

A triplet contains two or more segments of a gem, or different gems, that are joined by layers of glue. In a profile view, this image shows a thin seam of opal in the centre that is backed by dyed black chalcedony, and is overlaid (the domed area) by a quartz cabochon.

Although doublets and triplets are used to imitate natural gems, assembled stones are not always imitations. This is the case with natural opal, which sometimes occurs in layers so thin that they need reinforcement to be sturdy enough for use in jewellery. Black onyx, plastic and natural matrix have all served as the bottom layers of opal doublet or triplet cabochons. Opal triplets are topped with a transparent dome made of rock crystal, plastic, glass or synthetic corundum.