Blast spells do damage to opponents and/or objects. No spellcaster worth his ritually burnt tortoise shells lack this schtick.
Getting Blast Effects
Calling blast a sorcery stickis really misleading. It is listed as a sorcery schtick to show that sorcerers have access to it, but it is really bought as separate Blast schticks.
Sorcerers and Blast
Sorcerers tend to have many varieties of blast with few metablasts. This keeps the cost down. Sometimes they use "free" metablasts on some of their powers to give them specilaized effects. Of course, sorcerers are a diverse bunch, and some concentrate on just a few blasts with may metablasts instead.
Sorcerers may or not use Focused depending on taste. If they use a foci, it is usually a wand or staff.