One of the mistakes I made when I started making jewellery was not really understanding that different gemstones have very different properties, particularly with respect to durability. This means that some gems are fantastic for using in jewellery as they will effectively last forever, whereas others might end up being destroyed as soon as someone forgets to take their ring off while washing the dishes…
Durability is a result of a combination of properties that gemstones possess, including hardness, toughness and stability. Many people know that diamond is very hard, in fact the hardest gem that we know. It is also very stable, and as such has been used very successfully in jewellery for a long time. Diamond does have some weaknesses though. Because of the way its crystal is structured, it is susceptible to cleavage. This means that if it is knocked at a particular angle it may split. When designing and making jewellery, ideally the designer would take this into account. It is not feasible to remove the possibility of damage completely, but by taking care how the diamond is mounted and set into a piece of jewellery it is possible to give it some protection and to reduce the chance of damage.
Other gems are not quite as durable as diamond, and therefore more care must be taken, both in the design and wearing of jewellery. For example, emerald is very brittle, and can easily be chipped. Settings should surround the stone edges with metal to protect them, and wearers given advice about looking after their gems. Another example of a brittle stone is tanzanite. When asked recently about making a tanzanite engagement ring I advised against it, as the day to day wear of an engagement ring would not be compatible with trying to protect the gem. Opal is another interesting example. A soft stone, opal is sensitive to heat, water and chemicals, and is best used in occasional jewellery such as pendants and earrings with careful storage between wears, rather than in an everyday ring.
Whatever gem you are interested in, your jeweller should be able to advise you about appropriate care, and any limitations on their use in your jewellery.