I read a series of books a few years ago but I never finished the series.
The main characters were a brother and sister. The brother was jealous of the sister having put on a glove that does not come off and that summons a sword. Over time the brother learns magic.
The setting is like the Dark Ages(?). (edit) If anyone may have read the books, i remember the brother started using (fire?) magic in a mountain made of ice, and when the sister used the glove it would heat up, and would also burn if she tried to pull it off, and she though it was a curse. hopefully that helps.