Magnesium shavings are crackling ?

[50AE]

I've bough a bag with magnesium shavings 1 year ago. They seem to be true magnesium, they react vigorously with water when ignited. So I use them in fountains/gerbs and they perform very well. But one day I've been lighting small batches of the comp for fun and I discovered two properties :

 

-When a less-than-gram batch is burned on a surface and them the residue is rubbed, it makes small cracking sounds and it sparks.

-When a more than gram batch is burned, sometimes it produces a loud crack similair to dragon eggs after 1-3 seconds.

 

The composition is :

 

80 parts meal powder

20 parts magnesium shavings (10-20) mesh

[Miech]

I think it has something to do with the formation of unstable magnesium/sulfur compounds, similar to what happens with glitters. Another possibility would be a wet surface you are testing on. Then the crackling would be boiling water. I'm not a chemistry expert (yet) though, so I might be way off.

[Ralph]

I have found it crackles to though it dosnt seem to matter what ratios its in especially if it is a loose powder it crackles and sometimes spits