Yes it can be done but you need $, presses, and equipment
There is a video going around showing someone putting a hot coal into peanut butter, and it turning into a diamond or crystal. It seems too good to be true. It is. This is completely false.
I am not going to link to the video because I don?t want to reward them.
You can?t turn a coal and peanut butter into a diamond or crystal with ice, warm water, or any other household materials.
Yes with high pressure presses and equipment you can turn lots of things that contain carbon into diamonds. It just takes an extremely long time and costs an extreme amount of money.
A quote from the BBC future and io9
Frost hypothesizes that certain geological processes may draw carbon dioxide out of the world?s oceans and down into the mantle, where high pressure converts it to diamond.The key ingredient for this to happen, he thinks, is iron. The high pressures of the mantle force carbon dioxide from the rocks into the iron-rich minerals, which strip away oxygen, leaving the carbon to form a diamond. And that is exactly what Frost found when he recreated the process using his presses ? essentially forging a diamond from thin air.
Frost is hardly likely to make a fortune from his harvest; the diamonds take an agonisingly long time to grow. ?If we wanted a two-or-three-millimetre diamond, we would need to leave it for weeks,? he says. That hasn?t stopped him experimenting with other sources for his diamond maker, however; at the behest of a German TV station, he attempted to create some diamonds from carbon-rich peanut butter. ?A lot of hydrogen was released that destroyed the experiment,? he says, ?but only after it had been converted to diamond.?
So remember, if something seems too good to be true, it is.