Re: How many atoms are in a grain of sand?

Hi Roger,

Sand is mostly a compound of silicon and oxygen (SiO2) which has an RMM of 
60. As no two grains of sand are identical in size we must assume a 
standard volume. For the sake of this calculation I have assumed a volume 
of 1mm3. From tables the density of Silicon Dioxide is 2.3gcm-1 , so the 
mass of 1 grain of sand is 2.3/1000g. The avogadro constant (6 x 1023) is 
the number of atoms in one mole of substance. So,

(2.3 x 10-3 )/60= 3.8 x 10-5 

(3.8 x 10-5) x (6 x 1023) = 23 x 1018 atoms

Or 23 million, million, million atoms

Hope this has been of some help

David McEvoy


Admin note:

Dan Berger adds the following:

Actually the number calculated is for the number of SiO2 formula units
("molecules"). Since there are three atoms per formula unit, the number of
atoms in the grain of sand is about 70 million, million, million.