Why do the value of ruby, red spnel, and rhodolite-each one a beautiful red gemstone-differ? The reason is that they are different gemstone types.

Each type of gemstone has its own unique beauty. Each has its own characteristic hue and appropriate tone level. In the case of hue, for example, the bluish coloration of a beautiful purplish red rhodolite would be judged as a negative factor in a ruby. There are also mineralogical properties, such as hardness and durability, that have an effect on the polishing process, further contributing to the individual character of each gemstone type. Even within the mineral type beryl, it is well known that emerald is fragile and tends to chip easily, while aquamarine is more durable. One cannot grasp the value of a gemstone without knowing its type.

There are wide variations in mining production quantities according to gemstone type. Diamond, ruby, sapphire, and emerald are mined in limited quantities. About 120 million carats, or 24 metric tons, of diamonds are mined annually and about half of these are polished for jewelry use. However, when the portions ground away during cutting are considered, the total comes to only about 4 tons of polished goods per year. People around the world must share a quantity that amounts to less than a truckload.

When a stone is in demand, even low-quality material will be faceted, but if there is a surplus in supply, such low-quality crystals will be made into cabochons, beads, or carvings. Also, the range of cuttable material changes depending on whether it is treated. The polishing of gemstones involves a complicated interaction between the properties, demand, and technologies associated with each different type of rough material.

The supply of beautiful red spinels is very limited, and since supplies cannot be increased through heat-treatment, it remains more of a collector’s piece. The rhodolite pictured to the right is a beautiful, untreated purplish red color, but since it is mined in relatively large quantities, it is less expensive than ruby or red spinel. In this way, the value of different types of gemstones with similar beauty is greatly influenced by the prestige and mining quantities of each type.

There are currently about 50 different varieties of gemstones that can be classified by name. These classifications represent dignified gemstones, each with their own history, that have been accepted by people over time.

Hardness is an important feature when considering gemstone types. Quartz, with a Mohs hardness of 7, is common in nature, and there is a notable difference in the tendency for a stone to develop scratches depending on whether its hardness is above or below 7. There will be no need to worry about the hardness of something that is put on display in a glass box, but since gems are worn as adornments, hardness is critical.

Since reasoning led to the classification of gemstones by the German mineralogist Karl Emil Kluge in 1860. His writings separated gemstones into five groups based on mineral type, hardness, optical properties, and rarity of occurrence, and proved helpful in understanding the ranking of gemstones. According to Kluge, the first rank of gemstones includes those with hardness between 8 and 10. Emerald, despite its long tradition, is listed in the second rank because it is classified as the mineral type beryl. The fact that spinel is in the first rank and zircon is listed in the second rank further illustrates Kluge’s emphasis on hardness and transparency.

In compiling the list of modern gemstone classifications to the right, I separated the gemstone types appearing in this book and my earlier Gemstones: Quality and Value, Volume 1 into five ranks. Each gemstone was evaluated based on the three aspects of beauty, tradition, and hardness and durability (assuming ideal size and gem quality). By using classifications based on gemstone varieties such as emerald and aquamarine instead of mineral types such as beryl, some of the contradictions in Kluge’s ranking are resolved.

Peridot and tanzanite are gemstones with low hardness, but their beauty can be fully enjoyed with proper use. The degree of wear when they are set in rings compared to when they are set in pendants or brooches is much greater, and can be thought of in terms of decades.