Probably, not all magnesium blocks are made equal. I've been practicing with mine a while ago to good results. Sharp shavings works best for me. The primary advantage of magnesium - it will work on wet tinder, drying it. I'm in CA, that's not a huge plus here, so I switched to this fully enclosed composite solution:

http://www.campingsurvival.com/aufistflstan.html


Works perfectly well with practice and not deteriorating in salty ocean air at all. Contrary, that magnesium square block with flint I've been using, has started to produce a lot of grey dust in this climate, the flint became chipped and finally detached from the block.