Other Gemstones
Other gemstones are the coloured stones outside the sapphire family — tourmaline, aquamarine, garnet, spinel, zircon, amethyst and topaz among them — each a different mineral species with its own hardness, colour range and rarity. This is the connoisseur shelf at Ministry of Gems: stones we do not mine ourselves but hand-select, stone by stone, from the Ceylon cutters and dealers our family has worked with across three generations since the 1960s. Each is assessed and graded in Sydney by our FGAA gemmologist, with treatment stated plainly.
We do not mine these species, and we say so. What comes with them instead is our buying — direct from cutters our family has dealt with for generations, no trading floor in between — and our grading: full treatment disclosure on every stone, independent laboratory certification on request, and free lifetime re-authentication.
Common questions
Which coloured gemstones are hard enough for an everyday engagement ring?
Hardness is measured on the Mohs scale, where sapphire is 9. Spinel (8) and aquamarine (7.5 to 8) wear well every day. Topaz is also 8 but has perfect cleavage and can split on a sharp knock. Tourmaline and garnet (7 to 7.5), amethyst (7) and zircon (6.5 to 7.5) are better suited to pendants, earrings or protective settings.
How much does spinel cost per carat?
It depends almost entirely on colour saturation and size. In Australia, pleasant grey, lavender and steel-blue spinels commonly sell from about AUD 300 to 900 a carat. Fine pink and red stones of one to two carats typically run AUD 1,500 to 6,000 a carat, and vivid neon-pink or true red material can exceed AUD 10,000 a carat. Spinel is almost never treated, which is part of its appeal.
Is zircon the same as cubic zirconia?
No. Zircon is a natural mineral, zirconium silicate, formed in the earth and among the oldest minerals known. It has a high refractive index, lively fire and unusually strong double refraction, which makes the back facet edges look doubled when you view through the crown. Cubic zirconia is a laboratory-grown zirconium oxide simulant sold as a diamond substitute. Blue zircon is routinely heat-treated from brown rough, and we disclose it.
Are coloured gemstones heat-treated?
Many are, and it should always be stated. Nearly all aquamarine is heated to remove yellow-green tones; blue topaz is irradiated then heated, as natural blue topaz is rare and pale; blue and colourless zircon is heated; some tourmaline is heated or irradiated. Garnet and spinel are almost always untreated. Heat is stable and accepted; what matters is disclosure, and every stone we sell carries its treatment status in writing.
