Okay, I hope this will clarify some what.

All crystals are minerals - made up of various gases and chemicals.  All Rocks are made up of a mineral, combined with an "earth"grain and gas.

3 types of rock:

Igneous - originate from magma; cooled below the earth - classified as intrusive (granite)
                                                cooled above the earth - classified as extrusive(, obsidian)

Sedimentary - organic accumulation (rock slides, floods); mineral or composite moved by variable forces.
                                              They form slowly and in layers (coal, sandstone, shale)

Metamorphic - rocks that are changed by heat ,pressure or permeation (slate, quartzite, marble)


Metamorphic rocks (geodes) are where most crystals come from. Others are found in Igneous & Sedimentary rocks. When broken open or cut into the "crystals" are in RAW form.

Gemstones are the end product of these crystals after they have been cut, shaped, and POLISHED. The cutting produces the light refraction, the shape fills the desire of the individual and the polish removes scratches from polishing and gives sheen.

Geology is the study of rock, crystal and mineral.

Gemology is the study of the art of producing gemstones for use in jewelry, etc.

Does one have more power than the other? My opinion is no.
While a rock or crystal in raw for may be lager, it still holds many of the impurities that gave it birth.
And as a gemstone is small, it is refined, cleaned, highly refractive, perfect.

The difference is cost.
Raw is relatively inexpensive. Gem is relatively more expensive.

Also keep in mind what you want to use it for, gemstones are easier to carry of wear. Raw crystals are better for placement in the home or on the body.

You wouldn't want to lose a diamond rolling over when it's easier to find and use coal. (diamonds are compressed coal).

Hope that helped some.

awesome subject i was wondering this myself  actually...  so i took it in to search out some things myself  and found this below...  then ill type  why i like crystals so much myself..

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The combined art and science of studying, cutting, valuing, buying and selling precious stones. Some of the most precious stones that gemologists deal in include diamonds, rubies, sapphires and emeralds.

Gemology is spelled gemmology outside of North America.  
 
With advances in gemstone synthesis, gemology has become a much more important field of study. Gemologists value stones based on a number of factors, including cut, color, quality and clarity. When returns in the stock market decline, aggressive investors often seek out alternative investments that hold more promise of increasing returns on invested capital. Gemstone investing can appeal to people who want to make quick returns, but it is highly speculative and should be left to experienced professionals

and for what is crystal healing?

Crystal Healing - What is it?
Crystal healing is a form of healing that uses crystals or gemstones. The crystals are mainly placed on specific areas of the body called "chakras." Chakra is a Hindu term meaning spiritual energy. According to this teaching there are seven basic energy centers in the body, each having a color associated with it. Some crystal healers place the same color crystals as the color of the chakras on the person to enhance the flow of energy. Crystals are said to direct the flow of energy to the person in a particular part of the body and bring balance to a person's energy. Ultimately, they are used to cleanse the person from bad or negative energy believed to cause an illness. Clearing out the bad spiritual energy alleviates the physical ailment. Crystals are used for physical, mental, emotional and spiritual healing. Not only do people visit "crystal healers", in some places, professional nurses are being trained to use crystals for their patients. Additionally, crystals can be worn, placed next to a person's bed as they sleep, and in some cases placed around a person's bath.

here are the two links i found this bit of info  for others to inquire to lengthy

http://www.investopedia.com/terms/g/gemology.asp

http://www.allabouttheoccult.org/crystal-healing.htm

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ok now my version of it..

I loven my crystals for two or many reasons..  it helps me center  when im off balance..  2ndly im a strong believer in crystals  are warding off the dark spirits that try and attach them to me  without permission..  they cant handle the white bright light yeaaaaaaaaaaaaa ha!! feeeeeeel the power....
it has been tested in a ritual that happend last year with my soul twin and me and my bro and husband..  one tried to come near me but i was holding my crystal  they couldnt come into our circle becasue of our crystals.. i was holding mine..  i surely smelt them ohh boy  whew they stunk!  

other reasons  i use gem stones  and crystals  are  it energerizes me  and im one of them that gets  zappped by there energies lol...
i to am learning about them when i go to buy them  i walk around the shop and not touching anything  then all a sudden no word a lie i hear  take me take me take me so i go over to the crystals stare at em if i cant place a hand slightly above it to feel the energies..  if it zaps me then i know it called me to take it home lol...

other wise im still learning as to why im using my crystals so much  i dont even no half the time i just DO IT.

oh ps my soul twin and me and my totem animal white tiger we all share the exact same crystal  the six sided clear quartz point crystal..  my dragons love rolllin it off my hand it gives them the energy back as well as just playing with it..

Dragon's love and light

ps if you dont have a crystal  try and just purchase a small one  small ones have as much power as the larger ones....  its all how you use them..

namaste!

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Hi!

A gem stone is indeed a crystal but the powers and their ways of working are different! A crystal has indeed the properties of attraction and has an effect on water! They are stronger and dont work on planetary influences!

As far as astrology is concerned, I like to break from the path and i have noticed that the said norms of wearing stones in a particular finger or a particular metal dont really work! I check my cards for that and you will be surprised to note the different fingers they have suggested me for the different stones and it has worked for me!

However now, I just wear a bracelet of all the 9 gemstones which I find really pretty and beautiful and it works for me too!  

I go with the theory that if the crystal feels right then it is right.

There is nothing wrong in seeking crystals with certain properties and ofen do this in crystal healing, but when I need a boost I pick a bowl full of crystals and just pick the one I'm drawn to, either just to meditate on or look up the meaning - it can be a great divinatory tool to seek guidance for areas of life to focus on.

There is more to the gemstones whether they are semi-precious, precious are cyrstals (quartz).
Beyond what I have seen on this forum/board gems and crystal are much more than jewelry and related to astrology. As a Native American we believe that they have a spirit just as people do in fact all living beings no matter if it is a fish or rock it is from that kingdom and has so much to do with helping us two legged out(that's humans), We respect all things and as two legged most of the rest of the kingdoms cannot get from point a to point b without the help of us two legged or the wing ones or the 4 legged or the swimmers. Plants, trees, herbs all rely on the other kingdoms to help them in their journey on this big blue marble.
The Stone People rely on us to get to where they are going helping those on the way that need their help. Being a higher being they all have task to perform beyond astrology and jewelry. I carry a medicine bag everywhere I go filled with unprocessed stones and other items as well as they do changhe from time to time what I carry. I rely on them to let me know what it is I have need of that day. Because this is a two way street so to speak as we come and go so do they on this red road journey.
So to say only an eye clean or cut and polished , in gold only or silver only is not respecting the being that resides inside the stone.
I have much respect for all cultures and if this is the only way then so be it, but next time you are selecting a stone ASK THAT STONE FIRST what is best for them to help you on your path. and you will be amazed at what your new found friend has to say, and share with you.

Honor and Respect for all is what makes the world a better place.
A Mind is like a parachute it must be opened to work, so next time think of them instead of the self and a whole new world will open up