Crystalline Entity

A spaceborne life-form of unknown origin whose struture resembled a large snowflake, hundrets of meters across. The Crystalline Entity apparently thrived by absorbing the energy of biological life-forms on planets, leaving behind devastated planetary surface. The Cristalline Entity was responsible for the destruction of the Omicron Theta colony (including all inhabitans) in 2336. The andoids Data and Lore, who were dormant underground at the time of the attack, escaped harm. It was believed that Lore had betrayed the colonists to the entity just prior to the attack.
TNG "Datalore"
Colony residents Dr. Noonien and Dr. Julians Soong both fled during the attack aboard an escape pod, although Julina Soong was severely injured.
TNG "Inheritance"
In subsepuent years, Dr. Kila Marr, whose son died at Omicron Theta, studied the entity, examining 12 attack sites, including planet Forlat III. the entity's last attack was in 2368 at the Melona IV colony. Shortly thereafter, Marr destroyed the entity with a modulated graviton beam.
TNG "Silicon Avatar"
Star Trek Encyclopedia II