The Initiates meet underground monthly for services which include a homily, ritual dancing and group meditation for the alignment of purpose. During meditation and dancing, members strip to finely scented loincloths. Each month, one initiate is chosen (randomly, it is made to seem) to sacrifice his or her crystal to the cthuloid Scaled Tree which they worship. The sacrifice is accomplished by dropping the crystal into the pool in which the Scaled Tree sits, where the crystal dissolves. This initiate must then perform a quest assigned by the cult leadership; upon completion, the initiate is awarded a new crystal.
Every ten years, in the dead of winter, on a moonless night, a high ceremony is performed in an ancient stone circle. This ceremony involves a homily, meditation and extended ritual dancing, but involves an evocation instead of a sacrifice. The leader of the cult summons a cthuloid entity by means of a vile and murderous ritual made possible by the connections and resources of the noble cultists; it is rare for the same ritual to be used more than once or the same entity to be called up in more than one ceremony. The entity will then be sent to wreak some devastation which will not be equalled in the popular mind until the ceremony is repeated in another decade.
The Scaled Tree's stats are as follows, but it should be noted that the Scaled Tree will not reveal its motile capabilities unless credibly threatened; otherwise it will remain still, not even defending itself against ineffectual attacks.
Hit Dice: 3
Armor Class: 4 
Attacks: 4 branch swipes (1d6 dmg)
Saving Throw: 14
Special: Immune to normal weapons
Move: 12/6 ground/fly (4/2 in metric)
Alignment: Neutral (ironically enough, seeing as this cult worships Chaos)
This black, scaled, tree-like thing has no eyes nor any mouth. How it perceives the world around it is unclear; it has roots which absorb nutrients from the pool it sits in. The tree emits a constant, very low murmur which can only be heard if all else is silent. This murmuring is interpreted by the cult leader and is claimed to be the instructions concerning the quests of the cultists who sacrifice their crystals.
The cult is all that remains of the previous dynasty, overthrown a thousand years ago at the height of its decadence and self-inflicted weakness; it still ostensibly has the goal of overthrowing the current dynasty. Over 500 years ago, however, the cult was infiltrated and co-opted by those loyal to the reigning power. The current leader of the the cultists is an 18th level Magic-User loyal to the sovereign of the land. The cult is used primarily to divert the energies of those nobles disloyal to the king. The quests given to cultists usually are meaningless diversions, genuinely helpful to the people of the realm or are secretly for the benefit of the crown, though in the months before the decennial ceremony the quests usually involve acquiring the components for the rituals. The cult leader despises the noble cultists but relishes the free time leading the cult provides him, as he continues his studies in magic, especially concerning rituals to control cthuloid entities.
And now a word from our sponsors:
- The name of the Initiates of the Acerbic Crystal was generated with the first part of the excellent Arcane Order Generator.
- The cult itself was partly generated with an awesome two-page PDF by Nicolo Maioli called Unspeakable Cults and Secret Societies. I'm not sure if it's available anywhere, though it should be. Nicolo runs the Tower of Zordaz and The Yaqqothl Grimoire.
- The second part of the meat of the cult was provided by the excellent Mark II Weird Cult Generator, written by Brendan.
- Carcosa's Spawn of Shub-Niggurath tables provided the Scaled Tree.