Macademia nuts
Macadamia nuts are the seeds of the fruit macadamia. The macadamia is the hardest nut to crack in the world. There is a pressure of over two hundred pounds per square inch needed to crack this nut.

The hardness to crack the macadamia nut is one of the reasons why the price is so high, although the nut is nowadays more affordable than before. The macadamia is originally an Australian nut, discovered in 1857 by the Scottish chemist and physician John McAdam.
If you visit the plantation you can find macadamia trees. The nuts used to be processed on the plantation, but not anymore. Macadamia nuts grow at the Ijen Plateau in East Java, Indonesia.