In science this week we studied more rocks and did some more classifying. we broke open some igneous rocks and found that they are the only type of rock with crystals inside. sedimentary and metamorphic dont. we also found that the longer it takes to cool the bigger the crystals there are and there is less trapped air because it is all compressed out of it. we also took 8 different rocks and measured their hardness. we rubbed them against each other and saw which one left marks on the other. in addition to seeing which are harder we saw which can affect other materials like copper, a nail, glass and porslin. most of the rocks did not compair to the glass which was surprising to me but the hardest two did affect the glass while all the others just passed right over the surface.
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