In this article, we'll cover the basics of what you need to know about cat's eyes and star formations, how to spot them and what to look for when you're buying. So, keep reading to learn more about these unique and fabulous flaws.

What are "star" gemstones?

The star effect in most gemstones is caused by an optical impact typically referred to as an asterism. When a stone is cut in a nonfaceted style, like the star ruby, garnet or sapphire, it will often display a four or six-rayed star pattern.

This pattern can be best viewed using a strong overhead light and ideally should be centered on the stone when viewed from above.

What is a Cat's Eye?

The cat's eye is an optical effect created by inclusions or "flaws" inside the stone that mimic the look of a cat's eye. The cat's eye effect can be created by naturally occurring fibrous cavities, as is the case with the chrysoberyl cat's eye or basic inclusions and structures, like those found in quartz.

The cat's eye stone known as the chrysoberyl is a translucent, hard gem that ranges in color from a emerald green to a yellowish green to honey brown to close to honey yellow. It has an almost silk-like texture and, if cut properly, will display a brilliant line of white light right down its middle - giving it a cat's eye appearance. This unique gem was historically believed to ward off evil spirits and black magic and is quickly catching on today as a remarkable stone with a unique style.

Meanwhile, the quartz variety, which is typically yellowy-brown (tiger variety) or bluey-gray (hawk variety) is usually less striking and doesn't exhibit the same fiery liveliness as the chrysoberyl. The quartz versions of the cat's eye usually cost less.

When inspecting a cat's eye stone, appraisers look at it under a single, powerful light source from directly overhead. Usually, if the eye-line isn't directly centered, the value of the stone is reduced. Cat's eye is mined in China, Brazil and Sri Lanka.

How do I shop for a cat's eye or star gemstone?

When judging a cat's eye or star, you'll need a strong source of light to judge the light's effect on the stone. Typically, the stronger the light, the better.

Ideally, you want the cat's eye or star to be a distinct entity from the body of the stone and the size of this unique inclusion is also an important factor. Remember, the cat's eye or star should be as perfectly centered as possible; any asymmetrical effects can decrease the value of the stone.

If you don't have prior familiarity with the cat's eye or are uncomfortable judging its value on your own, you can certainly gain assistance from either a professional gemologist or appraiser.