A mineral that is the opposite of Talc?

Question

my niece(who i am the guardian of) is doing a school project and she has to pick a mineral, use a word to describe and find a mineral that is the opposite of it. She choose talc, and said weak as her word. She cant use diamond, unless that is the only one. so if there are any very strong minerals besides diamond please answer. Ten points if i prove it to be correct (:

Answer 1

Corundum (which includes sapphire and ruby) is almost as hard as diamond. Other "opposite" factors are clarity (talc is opaque, corundum can be transparent) and colour (talc usually white, corundum can be almost black)

Answer 2

Since talc is light and not very dense, something heavy and dense would fit the bill, I'd go with lead.  

Answer 3

Talc is a soft, hydrated metamorphic mineral, Mg3Si4O10(OH)2 with average density

So a hard, anhydrous mineral with either unusually high or low density would be the opposite.

Talc is formed though the hydration and recrystallization of mafic igneous rocks such as peridotite, gabbro, basalt et cetera at moderate (geologically speaking) temperature and pressure. By environment of formation, a mineral like gypsum or halite would be most opposite. These form at surface temperature and pressure though the evaporation of saline solutions.  

Sodium, Silica, Potassium and Aluminum generally behave oppositely to Magnesium, Calcium, and Iron. Thus, chemically, something like sodalite (Na4Al3(SiO4)3Cl) or potassium feldspar (KAlSi3O8) would be most opposite to talc.

The low end of Moh's hardness scale is defined as talc so in terms of hardness, something like diamond or corundum would be the opposite.