My understanding is that halogens are not only capable of getting
very hot, but also that they can break easily if the glass has
something on it like water or even finger grease (that's why you're
not supposed to touch the bulb).
We have some halogens that have an extra thick layer of glas over
them to hold the inside glass if it breaks, but these are to replace
the regular household lightbulbs (not for tanks) but I know that we
aren't supposed to use these outside because of the moisture causing
it to shatter when it gets hot.
Be very careful what you buy.