Diamonds are formed of carbon atoms. 12.01 grams pure carbon powder is known as one mole. The number of atoms in this one mole is 6.02x10^{23. }This number is known as Avogadro’s number.

The diamond with 12 milligrams (or 0.06 carat), has

$\dfrac {6.02\times 10^{23}\times 0.12} {12.01}$

$= 6.02\times10^{21}$

That means **0.12 grams** or 1**2 milligrams** Diamond contains $= 6.02\times10^{21}$ molecules.

In case of Diamond,

Number of Atoms = Number of molecules $= 6.02\times10^{21}$

Which means, it's a **6 with 21 zeroes** or **6 sextillions** or **6 thousand ****billion-billion** atoms in 12 milligrams of the diamond.