Yes larger ones do seem to have more strength to them but for the actual effect of the type of gemstone, any size will do. I like to make elixirs with some of my stones and use them as a tonic. I keep a red jasper and a quartz in my Brita water filter all the time and I find it gives me more energy.

My first experience with Moldavite was when my girlfriend gave me my lovely little piece. I was to give a presentation on sacred geometry and Fibonacci sequences at my college that day and I unexpectedly received it as a gift. I was given it about an hour before I gave my presentation, and I was EXTREMELY nervous about this presentation as I am a very shy person and have never spoken in front of an audience before without completely breaking down. I started to feel it's effects within the hour, I started shaking, my heart was racing and I felt energized like never before. When I got up in front of the class I just started spewing information like I had done this a thousand times, no nervousness, no trouble breathing or anything that would normally happen. I sped through my info and totally captivated the whole room. Afterward I got a long applause and everyone was congratulating me on my excellent presentation. I am not typically a high energy person but I was jumping around and getting really into it and everyone loved it. I was high on Moldavite for the next 2 days following that. I didn't even realize that it was caused by the stone, which I knew nothing about at the time, until I spoke with my now girlfriend who felt sorry for not warning me that that would happen! It can be very powerful so it is best to be prepared when obtaining it. I wrapped mine and wear it as a pendant, when I wear it with my Fire Agate beads, I am so energized I can do anything, that is a strong combination. One of my fav stones!