There will be 6 left. Take 1000 divided by 7 you get 142 and some Numbers. Then 142 time 7 which gives you 994. That's how many you gave out. 1000 - 994 equals 6 that is left over.
As the magma from the volcano rises up it begins to settle as crystals and causes the chemical compositions to change and the magma has less of magnesium and more of the silica contents.
A volcano that has more of silica oxide and a high temperature but low silica contents results in a more fluid or basaltic magma and a high content result in a viscous magma and they are of high explosive in nature like the Stromboli volcano and Mount Vesuvius.
