People often talk about precious stones as belonging to one group of stones and semi precious stones as members of another, as if there were a factual distinction. But in reality this is hardly the case. There is a thin and flexible line that divides these two categories. The above classification can be considered as something which has its origin in the past, since in some epochs and some cultures there was a strict distinction. In most cases those stones that were used in ceremonial rites and religious rituals were considered most valuable. In most case those were diamond, ruby, emerald, and sapphire. However, the notion of what is considered "semi precious" was different from one culture to the other, as well as the generally accepted knowledge when it comes to determination and classification of semi precious stones.
Let us take, for example, amethyst. In the past amethyst was considered precious stone, whereas today it is no longer a member of this family - it has be degraded to the family of semi precious stones. Why? Because of the large deposits of amethyst discovered in Brazil in the 19th century, this extraordinarily beautiful crystal has become more easily available and therefore no longer so "precious". We see that rarity is an important factor in determining which stone and crystal is falling into which category. Still when considering amethyst it must be said that this stone is indeed precious for many new age seekers and spiritually oriented persons, due to its metaphysical properties and invocational powers. Therefore we should consider not only material values and material semi precious stones qualities - the spiritual values and features should also be taken into account.
So what are semi precious stones types?
Traditionally, this is a vast category that comprises almost every other stone apart from diamond, ruby, emerald, sapphire, opal and pearl. There are some 130 types of stones, minerals and crystals that can be considered semi precious gemstones qualities. This means that in answering the question "what are semi precious stones" you can say that this category comprises at the very least the following crystals and minerals: amethyst, rock crystal, carnelian, rose quartz, topaz, aquamarine, agate, tiger's eye, tourmaline, aventurine, moonstone, jasper, citrine, ametrine, jade, howlite, hematite, malachite, obsidian, turquoise. There are of course many more types of crystals and stones not listed above. Even some specimen that do not (strictly speaking) belong to the group of minerals, like amber and jet stone, can be considered semi precious stones when producing jewelry. Almost every other stone can be listed in this category if only it can be obtained in relatively good shape in terms of its relative clarity, shape, color and general visual appeal.
Can diamond be a semi precious stone?
Almost every precious stone if not "pure" enough, (which means if it cannot prove good color, clarity, and luster) can drop down to a lower level and be considered semi precious. It is only due to their exquisite beauty and rarity that the precious stones (diamond, ruby, emerald, sapphire, opal and pearl) are considered precious. But you can also find specimens of lower quality from each of the above stone families. For example, you can buy 1 carat diamonds for as much as 100 $, but these specimen are then non transparent, purely cut and with questionable visual appeal. Sure, still they are diamonds, but they are no longer precious stones.
Can citrine be a precious stone?
The contrary is also true. You can have a precious stone quality of citrine, with amazing color, cut, brilliance, and clarity. The number of carats is not a decisive factor when we talk about extraordinary semi precious stones qualities, since larger specimens are also available. Of course, jewelry made of these types of semi precious stones can be extremely expensive.
Let us emphasize the most important conclusion of the above considerations: low quality diamond can be less expensive than high quality aquamarine, for example. This makes the question "whether or not a stone is considered semi precious" even much more difficult to answer. The personal wishes, budget and general background are also important.
There are many gem specimens with extraordinary quality, beauty, durability and glamour and all of them can be used to produce extraordinary jewelry.
So, as it must be clear to us now, "what are semi precious stones" is a question with no easy answer.