The November National Geographic has spectacular picts of a gypsum cave found in a Mexico lead/silver mine:
If such a cave were found like this but made of diamonds, would it be revealed or secretly destroyed? Tourist revenue from a preserved cave would be tiny relative to the revenue from carving it into diamonds for sale.
Diamonds don't form in caves. You would never find them in an environment like this.
Diamond formation is complex. I will try to dumb it down. First off, Diamond is elemental Carbon (C) that is metastable at low pressures (ie- Earth's surface) so usually the mineral with the composition of C on the surface is graphite. Anyways, starting in the deep mantle (~650 km) you have compounds like CO2, MgCO3, CCO. Mantle metasomatism (fluid movement) then moves these compounds through a transition zone into the upper mantle. This transition zone is thought to reduce (take away oxygen) these compounds and precipitate diamonds (mineral formula: C). These newly formed diamonds reside in the reduced upper mantle (~150-400 km). Reduced meaning there are low amounts of oxygen. If oxygen was present, even at these high temperatures and pressures, the C would oxidize into CO2.
So we have diamonds now, but they are realllllly deep beneath the surface. How do they get to the surface? Diamonds are brought to the surface/near-surface via kimberlitic magma tubes which are essentially direct shots from the upper mantle to the surface. Mantle plumes if you will. So they are found as crystals in rocks basically. Interestingly enough, diamonds are typically one age (lets say 1.5 billion years old), the kimberlite magma is (lets say ~250-30 million years old), and these magmas are emplaced onto stable continents that are roughly 2.5 billion years old. We have these old continents, fairly old diamonds, and young magma...meaning the diamonds must reside in that upper mantle for quite some time.
"What purpose does a market HAVE, if not to allocate resources according to demand?"
... and you think I have biases? It's obvious you don't give one wit about property rights. I already told you why. Suppliers aren't slaves. You don't just get to force them to provide for what people demand.
Humans are resources just like any other. Are you suggesting we bring back slavery?
"There's nothing intrinsically sacred about a market,"
Sure there is. A market arises naturally when rights are protected. When you violate the free market you are in fact violating peoples rights.