When I play survival mode in Minecraft PE I have following problems with mining:

1.When I mine (using a pickaxe) a block of an iron or nether quartz ore, these blocks disappear after mining completely.

2. When I mine a block of sand, this block shows up after mining but when I try to take it, it doesn't move into my inventory. 

Note: in the case of other types of blocks (lápis lazuri, coal ore, stone etc.), the game works fine and these problems do not occur