What is Prehnite?
Prehnite is a pale yellow-green stone made primarily of calcium and aluminum.
Some forms have iron in them as well, which causes a darker orange-yellow colour, but must of them are quite pale and milky.Its crystalline structure gives it a glittery appearance.
 
What are the benefits of Prehinite?
As a healing stone, prehnite is a very powerful protective stone for the body.
This is a stone that will do many useful things simultaneously.  Green Prehnite is both a heart chakra and solar plexus chakra stone. 
The solar plexus or power chakra is the seat of the will, and this green stone's action links your heart with your will, and brings you peace and joy, and will help to relieve worry.
Green Prehnite is one of the best healing crystals for you to utilize to help you to do the things that you want to achieve, from a heart based perspective. Prehnite is known to help aid with enhancing psychic gifts and abilities and is also good for meditation.
 
Why do crystals vary in shape and size?
Crystals are minerals that have grown into regular, geometric solids bounded by flat faces.In most cases, minerals grow into irregular, random shapes.