Zodiac signs are classified as earth, water, fire or air; Cancer is this type
The other triplicities are 
water signs (Cancer, Scorpio, Pisces), fire signs (Aries, Leo, Sagittarius) and 
earth... [DOC] [TLE] A Brief Introduction to Astrology: The four Elements - Astrodienst [PAR] ATradition sees the entire universe as consisting of the elements fire, air, water 
and earth.