What is a Star Stone?

A star stone is a gemstone which has been cut and polished in a way which takes advantages of natural inclusions in the stone which create a very distinctive star pattern when light reflects from the stone. Many star stones are sapphires, although rubies and many quartzes can be turned into star stones as well. These stones have historically been viewed with intense superstition, and they have also been highly prized, thanks to their rarity.

In order for a stone to be polished into a star stone, it must have a unique set of inclusions which are sometimes referred to as “needles” because of their fineness. Such inclusions can ruin a stone, depending on how it is handled and polished, and star stones require special care during the polishing process to ensure that they come out well. When the stone is polished properly and placed in the light, the inclusions catch the light and reflect it, creating a brilliantly rayed star.

Star stones are always cut in cabochon shape, meaning that they are cut and polished flat, not faceted. Cabochons typically have a flat back to make them easier to set. One of the most famous star stones is the Star of Bombay, a massive cabochon which was once owned by actress Mary Pickford. The stone is currently on display in the Smithsonian Museum, if you are interested in seeing a first rate example of a star stone.

The property which star stones exhibit is known as asterism. Asterism can take a number of forms, from a single line streaked across a stone to a complex pattern with a multitude of rays. As a star stone is brought into the light and moved, the pattern of the reflection will change, causing the star to slowly cross the stone. The distinctive rayed pattern will also be tinged with the deep colors and hues of the stone.

Because star stones are so distinctive and stunning on their own, most of them are set in very simple settings which emphasize the star design. The settings are designed so that they do not obscure the pattern of the star, and if other stones are used in the setting, they are usually modest, so that they do not distract from the focal point of the piece. Many star stones are quite large, making them suitable for necklaces, brooches, and heavy bracelets.

Frequently Asked Questions

What exactly is a star stone?

A star stone, also known as asteriated gemstone, is a type of precious or semi-precious stone that exhibits a star-like phenomenon known as asterism. This effect is caused by the reflection of light from needle-like inclusions of minerals within the stone, typically rutile or hematite, which are aligned in a specific way.

Which gemstones can display the star effect?

Several gemstones can exhibit the star effect, with the most notable being star sapphire and star ruby. Other examples include star garnet, star diopside, and star spinel. The quality of the star effect can vary depending on the stone's cut, size, and the density of the needle-like inclusions.

How is the star effect in these stones formed?

The star effect, or asterism, is formed when light is reflected off of parallel inclusions within the stone. These inclusions are typically made of rutile, a mineral made of titanium dioxide. When the stone is cut into a cabochon shape, with a smooth, rounded surface, the light reflects in such a way that a star pattern is visible.

Are star stones rare, and how does their rarity affect their value?

Star stones are relatively rare, especially those with a clear, well-defined star. The rarity of the star effect, along with the overall quality of the gemstone, can significantly increase its value. Factors such as the number of rays in the star, the stone's color, and transparency also play a crucial role in determining its worth.

Can the star effect be seen under any lighting conditions?

The star effect is best observed under a single light source, like sunlight or a spotlight, which allows the star to be clearly displayed. Diffuse lighting conditions can make the star pattern less visible. The sharpness of the star can also be an indicator of the stone's quality.

How should star stones be cared for to maintain their asterism?

Star stones should be cared for gently to preserve their asterism. It's important to avoid harsh chemicals and abrasives that could scratch the stone's surface. Cleaning with mild soap and water, using a soft brush, is recommended. Storing star stones separately from other jewelry can prevent scratches and preserve the star effect.