Pure essence can be made into high-level runes with the runecrafting skill.
You can't. If you're a member when you mine the essence it is pure essence but if you are just free-to-play then it just comes out as rune essence.
Pure essence can only be mined by members, above a certain level. Pure essence can also only be used by members for runecrafting. Pure essence is required for the more advanced runes (the runes that can only be crafted by members). For the basic runes, you can use rune essence or pure essence, but pure essence is more expensive, and therefore a waste.
There is no best, all pure essence is the same from every mine.
Pure essence is mainly used in 'RuneCrafting'. You use it to create runes at one of the many rune alters.
You use rune essence/pure essence on a altar. (runecrafting)
basicly normal essence makes onely normal runes but pure essence make combination runes learn about them here at this link http://runescape.salmoneus.net/runecrafting.html#combine
Pure essence can be used to create chaos, blood, death, soul, nature or cosmic runesANDAir, mind, fire, water, earth and body runes, which can be made using rune essence too.
There is no such thing as "Icon Essence" in Runescape. There is, however, Rune Essence and Pure Essence. Rune Essence is acquired by, after completing the F2P quest: Rune Mysteries, teleporting to the Essence mines and mining with either less than 30 mining or mining in a F2P world. Rune Essence is used to Runecraft Air, Mind, Water, Earth, Fire and Body runes. Pure Essence is acquired by, after completing Rune Mysteries, teleporting to the Essence mines and mining with 30 Mining and up on a P2P world. Pure Essence is used to Runecraft all runes, including the ones Rune Essence is used to Runecraft.
you must : be a member, be on a members world, and have lvl 30 mining. when you try to mine rune essence with these requirements you will instead automatically mine pure essence. which is worth much more
pure essence
The question is quite unclear, but if you mean, what type of essence is used to craft law runes in Runescape, you use Pure Essence. Hope that answers your question.
Anywhere you mine normal essence you can mine pure essencein members worlds. This is also true for monster drops, etc. You can't mine pure essence or get it in monster drops etc. in free worlds. You can get it from the grand exchange though.