Most people think diamonds are pure carbon, but actually, the majority of diamonds contain trace amounts of other elements, called impurities. The different impurities include nitrogen, boron, vacancies (a missing carbon atom), and line dislocations (which are part of a row aof carbon atoms missing).  Diamonds are classified into four basic types based on the relative presence of these impurities.

Type Rarity Colors

Type Ia Approximately 98% of all natural diamonds Colorless and near colorless are the most common colors of Ia, diamonds but all colors except blue are possible. 

Type IIa 1–2% of all natural diamonds

Colorless, near colorless, brown, and pink Heat treated ZSDA HPHT grown diamonds can be Type IIa

Type Ib Less than 1% of all natural diamonds

Yellow, orange, greenish yellow, brown, and combination of these colors ZSDA HPHT grown diamonds can be Type Ib

Type IIb Less than 0.1% of all natural diamonds

Blue and gray ZSDA HPHT grown diamonds can be Type IIb