Definition of niacin for English Language Learners. : a type of natural substance (called a vitamin) that is found in certain foods and that helps your body to be healthy.
Red diamonds are the most expensive in terms of money per carat, since red is the rarest colour of natural diamonds.
This necklace is the queen of all heart-shaped diamond necklaces. 8 Bulgari Blue Diamond Ring â $15.7 million. This ring is also one of the most expensive rings in the world as it costs $15.7 million. The price of $1.8 million per carat beats the previous world record price of US$1.68 per carat for a blue diamond.