First of all, I won't differentiate between "precious"* and "semi-precious" gemstones in this article. Here's why: The term "semi-precious gemstone" is an old and rather unscientific term. The terms "precious" and "semi-precious" can be very misleading, as they imply certain stones are more valuable than others, even when that's not the case. The distinction between the two terms was used to reflect a gem's rarity, quality and "beauty", and because there's simply no sure, objective way to tell which gems are "precious" and which aren't, you won't find them in this article.
So, I will simply talk of "gems" or "gemst