The BenBen Stone is a greatest rune device originally constructed in Atlantis.  It is the capstone of a magical stone pyramid and can only be used in conjunction with a Stone Pyramid, and by a Stone Master or Temporal Wizard with an Aberrant alignment.

Greatest Rune Device (Unique) 

IQ: 47 , communicates through full telepathy. 
Aberrant (very strict code of conduct and honor) 

The standard powers of lesser, greater & greatest rune weapons in addition to: 
Free Will Consciousness, 
True Trans-dimensional Object, Astrally Configured 
Magical Abilities: the being inside the BenBen Stone has the equivalent spellcasting ability to a 30th lvl Dragon & Tattoo Master, 24th lvl Temporal Wizard and a 15th lvl Stone Master & Rune Master. Knows all spells trough level 15 and Spells of Legend, plus Temporal and Stone Magic abilities. PPE: 46,500, replentishes itself at the standard rate. 
Psionics: Telepathy, Empathy, Presence Sense ISP: 350 

Travel via Pyramids as Stone Master or True Atlantean at no PPE cost. The Ben Ben Stone will only tolerate being bonded to a person who understands either Stone (Pyramid) Magic or Temporal Magic and will only activate itself when placed atop a Stone Pyramid. When placed as the capstone, the Stone Pyriamid and all of its powers come under the exclusive control of the Ben Ben Stone and its bonded user. No one else may use the pyramid for dimensional travel, healing or otherwise, without the consent of the Stone or the bonded user. It also causes the pyramid to become indestructible and temporally stable. The stone is domineering, ruthless and seemingly cruel, but extremely intelligent, patient and calculating. Its unfailing honesty and obsession with logic make it a formidable force in its own right. 

Anyone (this means anyone the stone wants) who touches the stone will suffer 2d4x10 MDC directly to hit points, or the BenBenStone may attack with it's formidible magic and psionic powers. 

The stone may cast a planet-wide Temporal Barrier once per day. The Temporal Barrier will prevent any temporal magic spells from being cast anywhere on the planet or in the atmosphere, or in orbit. This does not include the moon, or any terrestrial satellite in an orbit near the moon. Anyone attempting to cast a Temporal magic spell will have to make a save vs. magic. A successful save means that the spell did NOT work, but that the caster uses none of his PPE; a failure means that not only did the spell fail to work but that the mage lost his PPE.  It may be impossible for the caster to determine the reason for the spell's failure, roll the character's Principles of Magic skill to determine if the character can even guess why it didn't work. 

The stone, since it is placed atop the pyramid constructed at a Temporal Nexus Point, it can use the pyramid to open Temporal as well as Dimensional Rifts. Although the stone can do this, it very rarely does so, because it alone fully understands the inherent danger in its abilities. Also, the virtual absence of temporal energy (time) within the stone, causes the entrapped soul to be relatively unconcerned with the passage of time, or whether something happened, or will happen in the past, present, or future. Time passes with the stone, but a a greatlt retarded rate, 1 hour passes for each millenia within the stone, such is the perfect genius of this device. 

The most unique aspect of the stone is that it has a Free-Will Consciousness amd it's own conscience. It has a massive intelligence, advanced through eons of meditation, study and practice at long lost and arcane mental arts, and uses it to act according to its goals and motives. Those goals and motives are known only to the entity within the stone, the Chiang-ku dragon, A Kor. A Kor's history is irrelavant now, but it is known that he built this stone for himself. It is the product of his entire life's research into Runes and Temporal magic. Supposedly, A Kor used magic scavenged from the remnants of the Old Ones reign. He used a process unknown in modern times to construct the BenBen Stone. It was cut from a single piece of pure, solid Mithral. It was apparently tempered to an unbelievable hardness, and has acquired a gun-metal blue sheen. The rune combinations are all but endecipherable to modern Diabolists and rune experts. It bears none of  the usual characteristics of Splugorth or Dwarven manufactured rune devices, and appears to be a unique object. Its surface is covered in 46,500 individual runes, as well as four stylized chiang-ku dragons, one on each side of the pyramid, except the base. It measures fourteen feet high and weighs much more than expected. No crane, or mage can lift it, and anyone who has touched it has either died or ended up in the hospital. What can be determined is that the stone is very old and very powerful and very alive. 

The Stone is easily the equivalent of a powerful Alien Intelligence, or the most powerful of gods. Its willingness to work with lesser mortals (humans and Atlanteans) and the few supernatural beings that serve it, is because of one serious limitation. The stone is unable to move itself, and although immortal, does not possess a sense of the passage of time. It cannot Rift itself away, hide itself, or transform itself. It is fixed unless moved by another, and then only someone who the stone allows to touch it. It is also limited by its obsession, to restore the Atlantean nation, to correct the foul mistakes of the 'golden children of Atlantis' and rebuild the great Pyramid of Atlantis. These are almost impossible goals, but the stone doesn't care, it can wait. 

My basis for the use of the Ben Ben Stone: 

The Ben Ben stones were 'real', in as far as they were the ceremonial and practical capstones of the pyramids. I heard Dr. Zahi Hawass talk, last evening (January 20, 1998 at the Dept of Agriculture, Jefferson Auditorium) at a Smithsonian Institution Associates event, about discovering a BenBen capstone near the Great Pyramid at Giza. 
 

pages with references to BenBen Stones: