Are you
A Chemical elementMetal as the
The first letters of each Capiltalized word after 'I am' word is a Chemical symbol.
(The whole word can't be made from symbols e.g. sto in snowstorm isn't possible.)
Most especially per OP the first one or two letters of metal, or for the Capitalized words after 'I am' give Metalsfinal clue carbon, which is found in alloys which this puzzle also extends to.
I am Austerity.
(I = Iodine, Am = Americium), Au = Gold
Irrelevance.
Ir = Iridium
Curation in a Snowstorm.
Cu = Copper , (In = Indium, A = Argon) , Sn = Tin
Then combining Cu and Sn give the alloy BronzeBronze
Mnemonic
Mn = Manganese
the Schism
Th = Thorium, Sc = Scandium
Curiosities in the Allusive
Cu = Copper, (In = Indium, Th = Thorium), Al = Aluminium
Then combining Cu and Al give the alloy Aluminium bronzeAluminium bronze
Corruption
Co = Cobalt
Rebirth
Re = Rhenium
Ferocious Chaos
Fe = Iron, C = Carbon possibly giving Iron + Carbon = SteelSteel
The title 'A Rare Transition'
Relates to the Rare Earth and Transition metals