From the RuneScape Wiki, the wiki for all things RuneScape
A Teleport crystal is a small crystal which can single-click teleport a player to the elven village of Lletya. The teleport is reasonably close to a bank, the fruit tree patch and an altar. The crystal has four teleport charges when initially received and, when used up, becomes a Tiny elf crystal. It can then be recharged by Eluned for 150 - 750 coins; However she will only do this if it is out of charges and claims that she can only grant three charges due to her not being as skilled as the original enchanter. Players may possess multiple teleport crystals at the same time. Tiny elf crystals can be obtained as a common drop from elf warriors found in Lletya.
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After completion of Within The Light, Eluned can teach the player how to enchant the Tiny elf crystal further, thus enabling it to teleport the player to the Temple of Light as well as Lletya. This can be done by talking to her with a charged teleport crystal in the inventory. The Temple of Light teleport is very useful for reaching the Dark beasts near the Temple as well as the runite rocks. However, it should be noted that adding the second destination means that the crystal is no longer a one-click teleport. This enchantment extends to every enchanted crystal held by the player, in both inventory and bank, and is irreversible.
- The teleport crystal was once able to teleport people from any place to Lletya. (Even in level 50+ Wilderness) The crystal would also work while a person was teleblocked, thus making it the best safety teleport in the game. This glitch has been fixed.
- Regardless of the name: Tiny Elf Crystal, the crystal can hardly be referred to as tiny. The inventory image also gives the impression of a very small stone, however when droped the stone is rather large.
- During Within the Light, you ask if you can learn how to enchant crystals yourself (after enchanting the crystal in the Mourner HQ caves). Enchanting teleport crystals yourself could possibly be a future update.