Amethyst is the world’s most popular purple gem. It is the purple color variety of quartz that has been used in personal adornment for over 2000 years. Amethyst is the birthstone of February and an important New Age gem. It is used to produce faceted stones, cabochons, beads, tumbled stones, and many other items for jewelry and ornamental use.

Amethyst has a Mohs hardness of 7 and does not break by cleavage. That makes it durable enough for use in rings, bracelets, earrings, pendants, and any type of jewelry. Enormous deposits of amethyst in South America and Africa provide enough amethyst to keep the price low. Most people can easily afford amethyst.

While the word “amethyst” makes most people think of a dark purple gem, amethyst actually occurs in many purple colors. The purple color can be so light that it is barely perceptible or so dark that it is nearly opaque. It can be reddish purple, purple, or violetish purple. The first step in amethyst receiving its purple color begins during crystal growth. That is when trace amounts of iron are incorporated into a growing quartz crystal. After crystallization, gamma rays, emitted by radioactive materials within the host rock, irradiate the iron to produce the purple color.

The intensity of amethyst’s purple color can vary from one part of the crystal to another. These color variations, known as “color zoning,” are caused by varying amounts of iron being incorporated into the crystal during different stages of crystal growth.

Amethyst crystals grow slowly and the composition of the fluids delivering the iron and the silica needed for crystal growth can vary. The darkest color of amethyst forms when the largest amount of iron is incorporated into the growing crystal. That is what causes color zoning. Color zoning influences the marketability and value of amethyst. Most people want a gem with a rich and uniform color. As a result, gems of uniform color – no color zoning – are the most desirable and the most valuable.

The world’s most important amethyst deposits are usually found in the fractures and cavities of igneous rocks. In Brazil and Uruguay large amounts of amethyst are found in the cavities of basalt flows. Large cavities can contain hundreds of pounds to several tons of amethyst crystals. Smaller cavities, known as geodes, are often opened in a way that displays the crystals inside and then fitted with a base that allows them to be used as home or office decor. They are popular sales items at rock shops and mineral shows.

“Grape Agate” or Botryoidal Amethyst

In 2016, mineral dealers began selling specimens of “grape agate”. The specimens were composed of tiny purple spheres that ranged in size between about 2 and 8 millimeters across. The specimens were called “grape agate” because of their purple color, their botryoidal habit (from the Greek botrys, meaning a “bunch of grapes”), and because of their translucent appearance. “Grape agate” quickly became a popular new mineral specimen because of its wonderful color, fun name, and interesting appearance.

The material is not agate; instead, a more proper name would be botryoidal quartz. Even though the name “grape agate” is a misnomer, mineral collectors have hung on to the name because it is more fun and memorable than “botryoidal amethyst”.