Engram

Engrams are crystals; that are encoded with the patterns of armor, weaponry and other as-yet-undisclosed items. There are two known types of Engrams: Encoded and Encrypted.

Encoded Engrams are sold by the Cryptarch, and are coded with the patterns of known items, such as a particular section of armor or class of weaponry. Once purchased by the Player, the Engram is converted into a random example of that item by the Cryptarch. While decoding an Engram will generate a random item, it's still possible to know the type of item that will be discovered. Each Engram will indicate whether the item is armor, a primary weapon, a special weapon, or a heavy weapon. The quality of the item is also identified, as Engrams use the same color coding as weapons and armor: White for basic, green for common, purple for superior, gold for exotic.

Encrypted Engrams are defined in-game as having "unusual properties". These must also be taken to the Tower where the Cryptarch can be paid to convert them for a fee of Glimmer and (in certain cases) only after he has attained the necessary Rank. The Cryptarch is also known to have these rarer Engrams for sale from time to time.