Quicksand
Quicksand is the most stable kind of soil that exists. If houses and other buildings are built, this is mostly done on quicksand because of the unique characteristics of this soil.
According to urban myth, quicksand is a non-Newtonian fluid that is dangerous in the wild. The origin of this misconception is uncertain. Maybe the word 'quick' in 'quicksand' suggests, that there is motion involved in this type of soil. The idea that Newton would not have anything to do with this type of soil is as yet a mystery. While newtonian theories may be superceded and replaced by better theories, quicksand always stays as stable as it is.
If quicksand is mixed with enough quantities of water, the resulting material is commonly called a "rock". "Rock solid" thus refers to the excellent quality of quicksand that is mixed with sufficient water in order to turn it into such a rock. Gibraltar is often called The Rock. This is because it is very near the Mediterranean See, which supplies sufficient water to turn the quicksand into a rock.
The antonym of quicksand, slowsand, is a misnomer, as there is nothing slow about this kind of soil, just like there is nothing quick about quicksand. When timing the speed of these two types of soil under lab conditions, the velocity of both have proven to be approximately equal. Surprisingly, quicksand mostly wins the yearly soil races at Monaco. According to racing experts, this is sheer coincidence.
If one mixes equal part of slowsand and quicksand, the result is ordinary sand. Unfortunately, this process is irreversible. Attempts to produce valuable quicksand out of ordinary sand have failed so far, and some scientists hold that it is even fundamentally impossible to reverse the process. Since the year 2011 the production of artificial quicksand was boosted by new developments in soil technology. In practise, the quality of this artificial quicksand has proven to be insufficient, and many houses and other buildings that were built on quicksand since 2011 have collapsed.