Colored Gemstones April 01 2014
Diamond engagement rings have only been common practice for the last 75 years as a result of the diamond cartel De Beers' extremely successful marketing campaign to increase demand for diamonds. But what if you are interested in an engagement ring with a colored gemstone instead? Since rings experience more wear and tear than other types of jewelry, what are good options for colored gemstones on a ring that will be worn everyday? Well, to answer these questions is gemologist Roger Dery.
Something else to understand, when thinking about gemstones, is the Mohs scale of hardness. This characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. What is important to understand about the Mohs scale, is that it is a relative hardness scale, so a Diamond (which is a 10 on the scale) is about 4-5 times harder than Sapphires (Mohs 9), but a Sapphire is only about 2 times harder than Topaz (Mohs 8). So when someone says that a Sapphire or a Moissanite are second in hardness to diamond, there is a huge jump in hardness between the those stones and a Diamond, with the Diamond being much much harder.
Information from Roger Dery (For many of these stones he mentions "exposure", which means they will do better in a bezel setting, because less of the stone is exposed.):
Mohs 9 - Ruby and Sapphire: generally considered the most durable of the colored gems. If untreated in any way, will hold up very well in most all situations. Even those subjected to 'high-heat-only' still do very well.
Exception: Ruby that has been filled with substances such as glass have a much lower resistance to damage such as abrasion from wear.
Mohs 8-1/2 - Chrysoberyl including Alexandrite: in my experience Chrysoberyl holds up very well against wear. It does not exhibit severe brittleness seen in other gems - and would be a great stone for regular wear as a ring stone.
Mohs 8 - Spinel: is generally considered a gem that wears well. It is resistant to damage and not just damage from abrasion.
Mohs 8 - Topaz: can be worn in rings, but some caution should be exhibited. This is especially true with Topaz colored blue because it has been irradiated [and then subsequently heated]. This process has weakened the stone in some way that it does not hold up as well as Precious Topaz - which may, or may not have been treated at all.
Mohs 7-1/2-8 - the Beryl family including Aquamarine, Heliodore (golden Beryl), Morganite, Goshenite wear fairly well in a bezel setting, can be worn in rings though may not be suitable for 'everyday wear'. The heating of any of the Beryl's is done at a low temperature and it is not a factor regarding their durability. Beryl's do have an element of brittleness though not as severe as some other gems.
Mohs 7-1/2-8 - Emerald (of the Beryl family) is not well suited for everyday wear. A totally clean Emerald will hold up as well as an Aquamarine. But, finding an Emerald with that level of clarity is extremely rare. Roughly 99% of all Emeralds have been treated with a filler of some type to (usually) improve their clarity. The filler is likely to not hold up well over time. *Emerald's that have been treated should not be placed into an Ultrasonic cleaner, nor placed under a steam cleaner as this may affect the clarity enhancement substance. **Caveat: Emerald's treated with a specialized process known as "Excell" in the trade are known to have a higher level of durability over those treated with other methods.
Mohs 7-1/2 - Andalusite has reasonable wearability though it does have a slight brittleness. Facet junctions are likely to show wear after only a few years regular wear.
Mohs 7-1/2 - Iolite in my experience holds up fairly well for hardness 7-1/2. It does, however, have distinct cleavage and a sharp blow in one or more specific directions may cause it to separate into more than one piece. Though, when I have tried to do this in the rough, I have not been successful.
Mohs 7-7-1/2 - The Garnet group is generally thought of as reasonably durable. Facet junctions will show wear within the first few years of being worn. And, the facet junctions may not chip as much as 'crumble' for lack of a better way to describe this. Of the Garnets, the Andradite/Demantoid type is the least durable, and we have found the Pyrope/Almandine/Spessartite group seem to wear slightly better.
Mohs 7-7-1/2 - The Tourmaline group is suitable for rings, though not for everyday wear especially if the top of the stone is exposed. Tourmaline can be brittle, does not hold up well where temperature changes are radical. They are known to be 'chippy' as can be seen along facet junctions that are exposed.
Mohs 6-1/2 to 7-1/2 - Zircon is often thought of as brittle. Zircons heated to high temperatures (over 1,000*C) to convert them to blue are definitely more brittle and show the effects of wear easily. Blue Zircon worn high on a mounting will need refurbishing regularly. Unheated Zircons and those subjected to much lower temperatures (of various colors) are less prone to show wear - and appear less brittle.
Mohs 7 - The Quartz family (including citrine, rose quartz, amethyst, and smoky quartz) is well known due to being available and popular. Chipping along the crown facets is common, and abrasions from wear are as well.
*as a general rule, at least from me, I don't suggest wearing hardness less than 7 on a regular basis as the wear will become evident well before you expect it. I do suggest moving this type of gemstone into mountings offering great protection or off the fingers or wrist.
Mohs 6-1/2 to 7 - Kunzite is not a durable gemstone. It is brittle, does not resist scratching well, does not repair easily, and has perfect cleavage in two directions. In addition to all that, it has the unfortunate problem of being light sensitive - reducing its depth of color with prolonged exposure to direct sunlight. I have repaired my fair share of Kunzite's and I don't relish the fact that they show up waiting for my handy work. But since they don't wear well over time, they will all eventually need reconditioning.
Mohs 6-1/2 to 7 - Peridot does not share the fate of Kunzite, though its wear pattern is predictable. Abrasions are readily seen on exposed gems that are frequently worn - and fortunately, a refurbishing is not usually problematic.
Mohs 6-1/2 to 7 - Tanzanite is very popular and goldsmiths have taken to mounting them in lavish and risky ways. Exposed surfaces will show wear in a relatively short time and the perfect cleavage can be a problem. Tanzanite is also heat sensitive - even though it is well known to have been heated to acquire the beautiful blue to purple hues. It is the shock of rapid temperature change that may cause damage.
Mohs lower than 6-1/2 - Apatite, Opal, Pearls, Orthoclase/Sunstone, Scapolite, Sphene and Sphalerite and other low hardness gems all need special care to be worn in rings. It is generally accepted that these gems are best suited for pendants, pins, brooches or earrings.