Ceylon, which is now known as Sri Lanka, is known to produce alexandrite gemstones, although they are rare and not as well-known as Russian or Brazilian alexandrite. Here are some key facts about Ceylon alexandrite:

1. Color: Ceylon alexandrite is known for its distinctive color-changing properties. In daylight or fluorescent light, the stone appears green or blue-green, while in incandescent light it appears reddish or purplish-red.

2. Clarity: Ceylon alexandrite is typically highly transparent and can have fewer inclusions than some other types of alexandrite.

3. Origin: Ceylon alexandrite is mined in Sri Lanka, which is located in the Indian Ocean off the southeast coast of India. Sri Lanka has a long history of gemstone mining and is known for producing a wide variety of high-quality gems.

4. Rarity: Like all types of alexandrite, Ceylon alexandrite is rare and valued by collectors and jewelry designers. Its unique color-changing properties make it a particularly desirable gemstone.

The chemical composition of Sri Lanka alexandrite is the same as any other variety of chrysoberyl, which is an aluminate of beryllium with the chemical formula BeAl2O4. Alexandrite is a variety of chrysoberyl that contains trace amounts of chromium, which is responsible for its distinctive color-changing properties.

Here are some of the most famous Ceylon Alexandrites:

1. The Smithsonian Alexandrite: This is one of the most famous Ceylon Alexandrites in the world, weighing in at 65.08 carats. It is on display at the Smithsonian National Museum of Natural History in Washington D.C.

2. The Chrysoberyl Cat's Eye: This is a rare and unique Ceylon Alexandrite that displays a distinct cat's eye effect. It is a 121.65-carat gemstone that is currently owned by an unknown private collector.

3. The Rajah Alexandrite: This Ceylon Alexandrite weighs in at an impressive 70.21 carats and is owned by a private collector. It is considered to be one of the finest examples of Alexandrite in the world.

4. The Greenish Yellow Alexandrite: This gemstone is a 65-carat Ceylon Alexandrite that displays a distinct greenish-yellow hue in daylight and a reddish-purple hue in incandescent light. It is currently owned by an unknown private collector.

5. The Gauthier Alexandrite: This is a 23.56-carat Ceylon Alexandrite that displays a vivid green color in daylight and a deep red color in incandescent light. It was discovered in Sri Lanka in the early 1900s and is named after its original owner, the French gem collector Edmond Gauthier.