DND_Reborn
The High Aldwin
Why not? You can use metamagic when casting spells from a staff, for example, and I've never seen or read anything that implies you can't use metamagic on a scroll. After all, when you read the spell scroll, you are casting the spell.If you were using a spell, the diamond is not consumed, so you can cast it again after a long rest.
If you were using a scroll, they don't benefit from metamagic in the first place.