Scattered throughout the Land of the Lost, often found embedded in the walls of caverns and some pillars, are a variety of colorful brightly glowing Crystals. Certain crystals found in the caverns of The Lost City and in the Pylons are actually "fourth-dimensional nodes". Sizes vary from boulder-sized chunks to the more common walnut-sized gems, which themselves are merely chunks off the larger crystals.
Touching certain colors together can produce special behaviors, for example the red/green, red/yellow, and blue/green combinations. It is hinted in "Downstream" that blue crystals might be radioactive, or at least chemically toxic (Jefferson Davis Collie III tells the Marshalls that handling them will make them sick). Enik is able to configure the destination of Dimensional gateway using tables containing arrangements of these crystals. Their most common colors are red, blue, yellow, and green, though other rarer colors, such as white.
The Marshalls dubbed the crystals they found "light crystals". Enik later explained that they were called "fourth-dimensional nodes". They are apparently grown artificially or otherwise constructed by the Altrusians for use as a power source for their technologies. The larger crystals are possibly mildly radioactive and give off both heat and light as a byproduct of their nature. Rick Marshall theorized that they might even power the dimensional doorways.
Rick Marshall once lamented the number of possible combinations of crystals. In fact, there are six possible combinations of four colors taken two at a time, and four possible combinations of four colors taken tree at a time. The crystal matrix tables provide a 9x9 array, which would be capable of storing 162 bits (an astronomical number of possible states) if filled with crystals of four distinct colors.
The most common use of light crystals seems to be in crystal Matrix Tables, or simply as sources of illumination. On their own, the smaller crystals generally do not have special properties beyond their glow, but bringing two different-colored crystals together can cause additional effects in some cases:
- Bringing a red crystal together with a green one causes the pair to emit a blindingly bright but generally short-lived light; this combination is often useful for driving away Sleestak.
- Bringing red and yellow crystals together causes an explosion after a very brief delay.
- Putting two green crystals together (or possibly two like-colored crystals) is also an explosive combination.
- Combining red and blue do nothing noticeable, but adding a third, yellow crystal to the pair causes them to emit a near-lethal shock.
- In general, yellow crystals appear to trigger releases of energy from other crystals.
- A blue crystal and a green crystal together create a temporary force field a short distance away. This use was taught to the Marshalls by Enik in "The Stranger", but in the later episode "The Search", the Marshalls attempted to reproduce the effect and nothing happened (it's possible the crystals were dead).
- In general, blue crystals appear involved in telepathic functions. Blue crystals alone can under some circumstances hypnotize people into seeing what they love most.
Their are several crystal combinations:
- Jefferson Collie mentioned that blue crystals "make you sick", and discarded them when he mined them in his cave.
- In the Series Bible, blue crystals are said to have recording properties and can both record and play back "memories"