With the exception of the pearl, which is a shellfish, precious stones are minerals that possess traits of personal adornment. Precious stones originate from the most awesome powers of nature. They are found mixed around, in, under, and between the earths crust. Their beauty is concealed by their rough and worn outer layers, but their beauty can be brought to life by skilled and knowledgeable workmen.

Precious stones are so beautiful that kings and queens have worn them; men and women have looked upon them admirably, scientists have studied them, and poets have sung of them. Precious stones have been the fondest expression of love in all ages. The great Christian prophet John made the gates of pearls, and the walls of precious stones. They also endure through the test of time. Long after their original owners are gone the precious stone shines with pristine brilliancy. Time destroys nations, and reduces everything in them to ashes, but the jewels remain.

The two qualities that make precious stones so desirable is their beauty and durability combined. The beauty of a precious stone lies in its brilliancy, color, or both. The durability of a precious stone comes from a native hardness, which resists the abrasion of time and wear. Nature does not form all jewels fit for stones, some lack brilliancy, but they are valuable for there hardness and durability. Stones of this sort are valuable and used for their mechanical purposes.

The stones that are considered to be precious stones are the diamond, ruby, pearl, sapphire, emerald, Oriental cats-eye, opal, turquoise, alexandrite, and spinel. In the area between precious and semi-precious are andalusite, aquamarine, golden beryl, hiddenite, olivine, tourmaline, zircon, and the finer varieties of amethyst, topaz, and garnet.

In order to describe the hardness of stones a scale was devised by a German mineralogist named Moh. The scale ranges from 1 to 10, the larger the number, the harder the stone. The number attached to various stones do not designate absolute degrees of hardness, but are approximate. Of the same stone, some forms are harder than others. For example, one diamond may be a little harder than another. These variations are slight and no other stone at its hardest, approaches the softest diamond.

Many precious stones have a grain or cleavage, along the lines of which they can be split like wood. Some stones break easier than others. The optical qualities of precious stones when cut and polished are various. Among the different degrees are the power of reflection, most precious stones are doubly reflective.

Many precious stones are phosphorescent by exposure to sunlight, application of heat, or other electrical or mechanical methods. Some diamonds are more phosphorescent than others. In the quality of transmitting light precious stones are divided into four kinds, opaque, as jasper; translucent, as the opal and carnelian; semitransparent, as rose-quartz; transparent, as the diamonds, etc. Not all stones of transparent varieties are truly transparent. Many crystals and others are almost opaque. In some respects, precious stones are constant; they resist or are subject to heat or acids after their own invariable fashion. Many gems are very resistant to heat, and only change tints, but rarely changes shape due to extreme heat.

The colors of different stones are a lot of times almost identical. It is sometimes hard to tell what kind of stone it really is after cutting it. Sometimes even tests of hardness and specific gravity can fail. Fraudulent stones are always a problem and an issue in the gem world. Experienced jewelers can usually look at a stone and have a good idea what type it is.