Sri Lanka is well known for its high-quality sapphires, which are highly valued in the international gemstone market. Here are some of the characteristics and composition of Sri Lanka sapphires:

1. Color: Sri Lanka sapphires are known for their beautiful blue color, ranging from light blue to deep blue. Some Sri Lankan sapphires also exhibit pink, orange, yellow, green, and purple hues.

2. Clarity: Sri Lanka sapphires are often relatively clear making them highly prized for their clarity.

3. Cut: Sri Lanka sapphires are often cut in a variety of shapes, including oval, cushion, and pear.

4. Hardness: Sapphire is a very hard mineral, with a hardness of 9 on the Mohs scale, making it one of the hardest gemstones.

5. Composition: Sri Lanka sapphires are composed of aluminum oxide with traces of iron, titanium, and chromium. The amount of these trace elements in the crystal lattice determines the color of the sapphire.

6. Mining: Sri Lanka is one of the world's leading producers of sapphires, and they are primarily mined in the Ratnapura and Elahera regions.

7. Treatment: Some Sri Lanka sapphires may be treated to improve their color and clarity, including heat treatment to enhance color and fracture filling to reduce visible inclusions.

   Ceylon (now known as Sri Lanka) is another country that has a rich history of producing high-quality sapphires. Some of the most famous Ceylon sapphires include:

   1. The Blue Giant of the Orient: This is a 466-carat blue sapphire that was discovered in the Ratnapura district of Sri Lanka in 1907. It is considered one of the largest faceted blue sapphires in the world and is currently owned by an anonymous buyer.

   2. The Star of Adam: This is a 1404-carat star sapphire that was discovered in Sri Lanka in 2015. It is believed to be the largest star sapphire in the world and is valued at over $100 million.

   3. The Stuart Sapphire: This is a 104-carat blue sapphire that was once owned by King James II of England. It was originally mined in Sri Lanka and was later set into the British Imperial State Crown.

   4. The Blue Belle of Asia (also known as the Ceylon Blue Belle): This is a 400-carat blue sapphire that was discovered in the Pelmadulla district of Sri Lanka in the early 1900s. It was sold at auction in 2014 for $17.3 million.

   5. The Logan Sapphire: As mentioned earlier, this is a 423-carat blue sapphire that was discovered in Sri Lanka but was cut and polished in Burma. It is still considered one of the most famous sapphires in the world.

Overall, Sri Lanka sapphires are highly sought after for their beautiful color, clarity, and durability, and they are a popular choice for jewelry, especially engagement rings.