Platinum jewellery is always more expensive than gold jewellery due to its unique and rare qualities, but diamond jewellery is most expensive of all. It is a tough metal making it more durable and stronger than gold. The cost of diamond depends on 4Cs parameters i.e. cut, colour, carat, and clarity. Even if the diamond is smaller in weight but of excellent grading, it will still be costlier than gold and platinum being of greater weight.