There are no princes on earth who appear to be available for sale, sorry, especially one this small.
Generally, you would write .50 carat to represent a half-carat stone.
Half carat is the term used to measure the weight of the real diamond. A diamond's weight does not define or detract from the fact that the diamond is or is not a real diamond.
One carat weight of diamond weighs .20 grammes, so your diamond is about half that weight, or roughly half a carat.
A one-half carat diamond weighs 100 milligrams = 0.10 gram.
A half carat average clarity pink diamond can cost as much as 5,000 dollars. Pink diamond worth is dependent on size, cut and clarity.
You can buy a diamond of about this carat weight today on Blue Nile and pay between US$4,846 and US$60,820, depending on the cut, its quality, clarity, colour and exact carat weight that you want.
A half carat diamond of this cut measures 5.2 mm at the girdle; a .65 carat diamond measures 5.6 mm at the girdle. A certified gemologist can give you the exact carat weight of your diamond.
Depending on the cut, colour, clarity and exact carat weight, you could buy a diamond of about this weight today from Blue Nile and spend between US$17,000 and US$21,000. Then, you'd pay for the setting.
1 carat is 0.2g, so 1/2 of a carat equates to a 0.1g gemstone.
The descriptor '.45' usually documents the carat weight of a diamond: meaning 45/100ths of a carat, or nearly half a carat.
Carats in diamond weight can be divided into 100ths, meaning that a quarter carat stone could be described as a .25 carat diamond. In your case, you could describe this stone, as just over half a carat or .58 carat diamond. Less than full carat stones are also called points: a 58 point stone in your case.
The value of a diamond depends on its cut, its clarity, its colour and its carat weight. A local jeweler can give you the answer you want.