Many people will put their hand in the box and let the crystal choose them. Like people, each crystal is unique and may have many different characteristics. There are female and male crystals. There are single pointed and double terminated crystals as well as different shapes. These all can effect their energy flow as well as their purpose.
Male crystals are usually clear and crisp, while females are almost opaque or cloudy.
You may find that many crystals will have parts that are of both male and female energy which can be a perfect Yin and Yang balance. This combination is very common in clusters. The energy of crystals with a single point at one end usually flows in the direction of the point. Some people don't care to work with cut and polished crystals or gemstones as opposed to them in their natural state. Others, especially gem healers, primarily use cut and polished gems and stones in their work and some gem literature suggests that certain stones be cut, faceted or polished to intensify their healing properties.