Across
1
Substance with pH below 7
3
Curved glass that refracts light
5
Preserved remains of ancient life
6
Mass per unit volume
7
Second lightest element
Down
2
Naturally occurring inorganic solid
4
Magnetic metallic element
8
Force that attracts objects together
9
Our home planet
10
Unit of energy
11
Amplified beam of light
12
Ball of burning gas in space
13
Group of similar cells