Germanium

Germanium is the most scarce element of the carbon group.
But it may be the most useful in advanced mechanosynthesis with …

• its tetra-valency and
• its bindnig strength that is neither to high as (as with carbon) or to low (as with lead or perhaps tin)

For advanced mechanosynthesis germanium is needed only in extremely low trace amounts. So low abundance is a non issue here.

As structural material

As a structural material it's rather unsuitable due to its low abundance.
It forms an oxidic mineral in with the tetragonal rutile structure called argutite just as all the heavier elements of the group do (and silicon does under extreme conditions as seen in the mineral stishovite)

• Argutite GeO₂ (Mohs 6-7; ~6.28g/ccm; tetragonal; rutile structure)

Related

• See: tooltip chemistry & tooltip preparation zone
• Group neighbours: Carbon, Silicon, Germanium, Tin, Lead