What are the main types of cultured pearls and what are their distinctive characteristics?

Akoya pearls are the small white pearls that most people picture when they think of pearls. They are saltwater pearls, and are usually round and white or cream, with a pink overtone and high lustre. They are typically less than 9.00 mm in diameter.
 
Tahitian pearls are often referred to as “Black pearls”, however they actually occur in a wide range of dark cool colours, the most common being greenish grey. They are saltwater pearls and typically range in size from 8.00 mm to 14.00 mm, and while they are most often round, they can occur in any shape.
 
South Sea pearls are the largest of the cultured pearls, and are usually white or varying shades of yellow, often referred to in the trade as “Golden”. They are saltwater pearls and typically range in size from 8.00 mm to 18.00 mm, and while they are most often round, they can occur in any shape.
 
Freshwater pearls typically occur in a wide range of pastel colours (primarily variations of pink and orange), but some have multicoloured or metallic appearances. While they are most often found in smaller sizes, and in near-round or oval shapes, they can occur in a wide range of sizes and shapes. Smaller pearls are usually non-bead cultured, while larger freshwater pearls are often bead-cultured.
 
*While each of the pearl types have inherent typical size and colour ranges, pearls can occur outside of those ranges in all pearl types.