Small accent diamonds referred to as melee range from .001 to 0.18 carats... The Value of Melee Here is a site that has some prices but not from a stone as small as you mention. White Diamond Melee Since your stone is smaller than the smallest available on this site - 0.01 carat / 1.3 mm which sells for approx $3. read more
Carat weight = 4 x 3.5 x 2.5 x 0.009 = 0.315 ct Keep in mind that all these formulas will give you estimates that are only approximate. If you want to get an exact value for the carat weight of a diamond, you should weigh it with a scale, preferably one that shows milligrams. read more
A 1-carat diamond that is internally flawless, perfectly cut, and “D” color could be worth over $20,000. On the other hand, a diamond of the exact same size that is significantly included, has a “good” cut, and a “J” color could be worth under $3,000. read more