The corundum family, a group of gemstones including ruby and sapphire, is known for its exceptional hardness and vibrant colors, with ruby being the red variety and all other colors (including colorless) being called sapphire. 

Here's a more detailed look at the corundum family:

• Composition:Corundum is a mineral species with the chemical formula Al2O3 (aluminum oxide). 
• Gem Varieties:
  • Ruby: The red variety of corundum, typically due to the presence of chromium. 
  • Sapphire: All other colors of corundum, including blue, pink, green, yellow, orange, and colorless, are considered sapphires. 
  • Padparadscha Sapphire: A rare pink-orange variety of sapphire. 
• Color:The color of corundum gemstones is determined by trace elements present in the crystal structure, such as chromium (red for rubies), iron and titanium (blue for sapphires), and others. 
• Hardness:Corundum is one of the hardest minerals, second only to diamond, making it highly durable. 
• Other Corundum Varieties:
  • Green sapphires, parti-sapphires, and pitambari sapphires 
  • Phenomenon stones, including color-change sapphires, star sapphires, and star rubies. 
• Significance:Corundum gemstones have been highly valued and sought after for their beauty and durability, with rubies and sapphires being among the most important colored gemstones for centuries. 
• Notable Locations:
  • Sri Lanka is known for its sapphires, including the blue variety. 
  • Myanmar and Thailand are known for rubies. 
  • Kashmir in India is known for its unique blue sapphires.