Opal is considered lucky because it displays all colors. This gemstone trait is described as which of the following?

• A. Glows in the dark
• B. Is the hardest gemstone
• C. Has no color variety
• D. Displays all colors

Answer: (D)

The main idea here is opal’s play of color. Opal doesn’t have a single color; instead, its internal structure of tiny, regularly arranged silica spheres diffracts light, splitting it into a spectrum. As you view the gem from different angles, you see flashes of many colors—often the full range—so it appears to display all colors. That broad color display is what people describe when they say opal shows all colors. The other statements don’t fit this phenomenon: glowing in the dark would be a different property (phosphorescence), opal isn’t the hardest gemstone, and opal commonly shows color variety, not a lack of color.