Number 11 pretty much answers number 3:
Quote:
3. Heavier Elements on Surface: Normal planetary composition results in heavier elements in the core and lighter materials at the surface; not so with the moon. According to Wilson, "The abundance of refractory elements like titanium in the surface areas is so pronounced that several geologists proposed the refractory compounds were brought to the moon’s surface in great quantity in some unknown way. They don’t know how, but that it was done cannot be questioned." (Emphasis added).
11. Unusual Metals: The moon’s crust is much harder than presumed. Remember the extreme difficulty the astronauts encountered when they tried to drill into the maria? Surprise! The maria is composed primarily illeminite, a mineral containing large amounts of titanium, the same metal used to fabricate the hulls of deep-diving submarines and the skin of the SR-71 "Blackbird". Uranium 236 and neptunium 237 (elements not found in nature on Earth) were discovered in lunar rocks, as were rustproof iron particles.
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Although titanium is found in both the highlands and the maria, the concentrations of it typically are minimal in the highlands and much higher in the maria. The titanium is typically bound up in the mineral ilmenite, which is more abundant in the basaltic lavas of the maria.
As Peter pointed out, the lunar crust actually is lighter than the mantle and the core, contrary to the assertion in item 3 above. The crust is composed mostly of lighter-weight minerals that make up rocks such as anorthosite, norite, and troctolite. Sometime after large impacts carved out the basins, parts of the mantle melted (or were molten) and some of the heavier minerals from below flowed up to the surface.
The existence of titanium at the surface does not rule out differentiation (the planetary process whereby heavier minerals sink and lighter minerals float to the surface). The heavier titanium is mostly localized to the maria.