1.2.4: Synthetic Minerals and Simulants

1.15 Synthetic zeolite

According to the definition given above, minerals must form by natural geological processes. However, synthetic minerals are commonly made for industrial or commercial use. For example, zeolites sold as health products, such as the product shown here, are generally synthetic. And, because zeolites are natural sieves and sorbents, synthetic zeolites are used in water softeners and in chemical manufacturing processes. The synthetic zeolites are fundamentally the same as naturally occurring minerals – they share many of the same properties – but are prized for engineering and industry because they have purer compositions and more consistent physical properties.

Gem	Mineral
ruby	corundum
sapphire	corundum
diamond	diamond
emerald	beryl
aquamarine	beryl
amethyst	quartz
citrine	quartz
alexandrite	chrysoberyl
moonstone	K-feldspar
topaz	topaz
zircon	zircon
opal	opal

And, we make many synthetic gems, too, today; we have been doing so for almost 150 years. Some of these “fake” gems are beautiful and valuable. Common ones include ruby, sapphire, diamond, emerald, amethyst, citrine, and alexandrite. The table on the right lists these gemstones and others that may be synthesized, along with and their mineral equivalents. Some of the gems have the same name as their mineral equals; but many do not. Ruby and sapphire are both varieties of corundum, amethyst and citrine are varieties of quartz, emerald is a variety of beryl, and alexandrite is a variety of chrysoberyl.

Manufacturers also make other gem-like synthetic crystalline materials that have no natural mineral analogs. They are commonly called simulants and include, among others, forms of cubic zirconia, titanium oxide, and strontium titanate that look something like diamonds. Synthetic gemstones and simulants are often of high quality and mimic natural minerals well – they may be unflawed and more perfectly formed than natural gems. Distinguishing synthetics from real minerals can be quite challenging. For this reason, some people do not distinguish between synthetic and natural minerals.

1.16 Natural corundum

1.17 Synthetic rubies

The two photos of red stones (left) are natural corundum from Tanzania and synthetic corundum grown in a laboratory. The synthetic corundum was faceted (ground) to give it flat faces and sparkle. We call red varieties of corundum, like the corundum shown, ruby. Corundum of any other color is called sapphire. Blue sapphires are most common, but pink, yellow, and other colors exist.

1.19 Natural topaz crystal

1.18 Irradiated topaz

The blue stone in Figure 1.19 is natural topaz from Sri Lanka. Strong aquamarine blue is a rare color for topaz, which is typically clear or light colored. So, most commercial blue topaz is treated to create its blue color. The faceted stones in Figure 1.18 are natural topaz that has been irradiated. Note that the natural topaz, and the natural corundum above, contain smooth crystal faces that formed as the mineral crystallized. The faceted topaz and corundum stones have planar surfaces created by grinding and polishing. The compositions and crystallinity of synthetic corundum and other synthetic minerals are nearly identical to natural specimens, but the synthetics are not considered true minerals. Mineralogical purists would also argue that minerals that have been altered, such as the topaz crystals in Figure 1.18, are no longer true minerals.