By definition a crystal is a solid substance formed by a collection of atoms called the Unit Cell that is repeated in exactly the same arrangement over and over throughout the entire material. When a crystal is free to grow without constraint or interference, it is bounded only by its crystal faces. The geometric pattern or shape of the crystal faces reflects the internal atomic arrangement of the crystal structure.
To most people the word “crystal” means perfect,  “I can hear you crystal clear…” But is a crystal really 100% perfect?!
Well, this may be true for a well controlled lab-grown synthetic crystal. In the real world, chaos and randomness occurs.
A natural crystal is defined as a homogeneous inorganic solid which possesses a definite, but generally not fixed, chemical composition and a characteristic internal atomic structure. The chemical composition may vary within given limits (ie atomic sizes, valency). A good example is an isomorphous series crystal such as garnet. Sometimes some structural crystal damage may also occur which may become a color center (ie type IIb tinted yellow diamond). Futhermore, there are additional impurities which provide colors and inclusions to allochromatic crystals (ie chromium in corundum crystal make it red).
Twinning and other growth structures (ie growth lines, feathers) also made them imperfect. Not to mention, crystal, liquid phase, gas phase inclusions and their combinations.

Thank you Agianto for this info.

I read somewhere the crystals produced in laboratory does not have same healing effect(means less efficient) than those obtained naturally.I was wondering what is the reason behind.Would be interesting to know.Maybe they don't have life in them as the natural ones got.

dhav

Dhav  lab grown specimins are far younger obviously, some may be a few days old and so have very few memories or energetic layers. They are not the same energetic compostion as natural crystals formed over aeons of time

Thank you Gem for helpin out about this question.Now i get it and it's true what you said.

Gem has a point. But there are many other beliefs. Some believe natural crystals are natural energy resonators because of their simplicity and orderliness. Some believe that  the energy of the natural crystals came from the ever changing (heat and pressure) earth plate tectonic, giving each crystals different growing "life" experiences. The Indian vedic people has many versions. Some believe the natural crystals on this earth were the results of the condensation of the rainbow cosmic rays thus having their respective energy......