Diamonds cost so much because they are rare. You won't just find them on the sidewalk in NYC. It takes hard work to find the diamonds, so the guy who found the diamond should get paid good money for it.
Diamonds are mined to recover them for use. As there is a good deal of demand for them, they have significant value. It is a simple economics principle that if there is demand for something, a supply chain will appear to deliver the goods.
Larger diamonds are sought after for use in jewelry, as you could have guessed. But there is a large demand for diamonds for use as a material for cutting and for abrasives -- about 75% of all diamonds mined.
Diamond, as you recall, is the hardest substance known, and it is many times harder than anything else. This makes the use of diamond absolutely necessary in industry. Its vital. A slurry or paste of finely divided diamonds can be used to grind or polish anything you can think of. Oh, and only diamond abrasive can be used to polish those diamonds you see used in jewelry.
Smaller diamonds that are unsuitable for use in making jewelry are also used to make cutting tools. Blades or cables impregnated with small diamonds are used to cut concrete, rock and other very hard materials, including many hard metals. The industrial diamond supply is monitored by all developed countries as this form of carbon is considered a strategic material. Our need for diamonds as jewels or industrial material fuels all recovery operations.
Diamonds cost and weigh on an individual basis.
Given the high number of diamonds limited by the low carat weight in your question, the cost of the diamonds might not be so much a factor as the quality of the setting into which they are mounted. The clarity quality that you describe wouldn't be so visible in diamonds weighing less than a quarter carat (.25 carat) each.
Today black diamonds are sold for prices that are comparable to those of white diamonds.
They actually cost diamonds now. They used to cost 1 pass.
It is usually the cost of the mounting.
No. Imagine how much that would cost.
Even then, diamonds were valued by their individual cut, colour, carat weight and clarity. Since 1990, the value of diamonds has increased, as a general rule.
The cost of a diamond depends on its value, which is determined by its colour, clarity, carat weight and cut.
Prices are changing alot for diamonds, but right now an uncut diamond's price is 10,600 gp.
Diamonds always cost more than gravels.
The diamonds on the ring may be more valuable than the ones on the necklace.
Your answer depends on the quality and size of the diamonds.