Is Cristal cave in Oklahoma USA natural? What are the evidences?

Question

...the rock is very hard, and there's no traces of water. How it's formed? I think it's not natural)

Answer 1

This is a very common name for caves, so it is hard to be certain of which Crystal Cave you are asking about. There is a Crystal Cave near Cherokee County that is part of a cave preserve that is most certainly a natural cave. It is gated and locked and not open to the public as far as I know. I can find no references to a "Cristal" Cave.

It is not uncommon for a cave to have formed during a period of time many thousands or even millions of years ago when the climate of a the area was much different than it is today. For example, during the Eocene about 38 million years ago the area where Oklahoma is now had a paratropical climate. (see: http://www.scotese.com/earlyeoc1.htm)
There are many caves in desert climates that formed long before the area became a desert. Consider some of the spectacular caves in southern Arizona such as Kartchner Caverns:
http://www.pr.state.az.us/Parks/parkhtml/kartchner.html

In the northwest part of Oklahoma there are many caves formed in gypsum. In other parts of the state there are caves in limestone. The hardness of the rock has nothing to do with the formation of a cave. In both limestone and gypsum, caves are formed by dissolution of the rock by water. In limestone caves this process is aided by carbonic acid which forms in overlying soil when rainfall dissolved carbon dioxide. This acidic water attacks the limestone and forms caves. Limestone frequently has fractures and joints within the rock that are the initial paths of water flow, and as these enlarge they form connected paths that often grow into a cave. If the process goes on for enough time, the limestone dissolves away completely. However, in many cases the cave forms and then climatic changes or changes such as geologic uplift bring cave formation to a halt. The cave is preserved and is no longer actively forming.

To see some more informatin about cave formation:
http://www.speleogenesis.info/

Here is an animation that illustrates perfectly how a cave can form and then become dry:
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1405/es1405page01.cfm?chapter_no=visualization

Answer 2

First the correct spelling is Crystal.
Yes, crystal caves are natural formations.
Over millions of years water containing large amounts of dissolved solids seeps through the rock and crystals slowly grow. The type of rock that water is seeping through dictates what type of crystals grow.
Quartz crystals are Silica, Dolomite and Gypsum crystals are Calcium.

Answer 3

anything