"Silicon Avatar"
The Enterprise gives chase to the Crystalline Entity after it destroys a Federation colony. A xenologist, who has a motivation all her own with respect to the Crystalline Entity, is assigned to the Enterprise to assist in the investigations.
"Lieutenant Worf, I don't think I've ever seen a more beautiful sight." - Riker
The Crystalline Entity is a huge, spaceborne lifeform whose body consists of a complext crystalline structure similar to a snowflake in shape. This organism is considered a massive planetary threat. It travels through space using a natural warp travel ability, visiting life-supporting worlds and feeding on the entire biosphere. It consumes matter from a planetary surface by emitting a powerful ray which destroys everything organic and converts it into energy for the entity's metabolism. This 'feeding ray' is able to penetrate rock and earth, devouring all fauna, flora and microbial life, even in the underground. This species' workings have been compared to a giant, living electromagnetic collector.
"The sperm whale on Earth devours millions of cuttlefish as it roams the oceans. It is not evil. It is feeding." - Picard (Defending The Entity's Nature)