A hot rock massage is a powerful form of massage therapy used to relieve stress and unwind tight, fatigued muscles throughout your system. During a hot stone massage, tender, flat rocks are placed on particular regions of the body. The stones are usually made of basalt, a normal kind of natural volcanic stone which retains warmth even in cold temperatures. Basalt rocks vary in colour from purple to black and come in many different sizes, from small to big enough to cover the entire foot. Some basalt stones may have small holes or irregularities which may be present, which might affect the massage's efficacy.