These rock crystal prisms are called singing crystals, due to the high pitched sound that they emit when shaken around.You can tell it is a Singing Quartz due to the sound they make as they hit each other, it is a clear sweet tone rather than the normal clunk of quartz hitting quartz.  The high pitch sound of the crystals is said to make the ohm sound and is said to be created by extraterrestrials or higher vibrational beings in order to make contact easier with them and to send us messages when we are ready to unlock the knowledge.  A wonderful experience is gained by meditation on the sound of the crystals touching each other.  They are an uplifting stone that makes you feel light and realize that no matter how difficult things seem everything is going to be ok.

They do not all make the same pitch when struck, if you are musically minded you will find that there is a variation between each point

These rock crystal prisms are called singing crystals, due to the high pitched sound that they emit when shaken around.