I have used with great success purified Shilajit that originates from Altai mountains (it is called Mumijo locally, Russian name for Shilajit) and is sold in small bricks of 25 - 50 grams.
It is pure black, and has the specific smell of bitumen mixed with very dark chocolate. The taste is very bitter. It gets soft in the hand and hardens when temperature drops below 20ºC. When softened one can draw a very long thread from it, it will not break. The seller recommends not to warm it more than 38ºC as it will lose a lot of its qualities. It should not be processed with metal tools or in metal plates/bowls and the like. It is sold together with a 5 page recipe folder listing many remedies to be fought with Shilajit / Mumijo. The proof of the pudding is in the eating has been said, and having tried this Shilajit I can confirm it does what is told about it. I first experienced a detoxing process, which made me doubt the quality as I felt not too good, but once I realized what was going on I relaxed and after a few days I could feel vitality as I never felt before! I have the habit of working out in the gym and I had stopped doing so for two months. When I started my exercises again, I was surprised: no muscle ache which one expects to feel after two idle months, and more endurance than ever before ! I can only contribute this to the Shilajit! I took half a gram daily with water (the seller gives the traditional water solution method of 30% shilajit and 70% distilled water, the shelf life is unlimited and it is easy to consume, but I like to experiment). The seller is active at this website for those interested. I can recommend this source full heartedly !
I had tried tablets and capsules before but they were disappointing. My assumption is that the processing involved in tablet-making or producing powders destroys many powerful components in the Shilajit (assuming it really is Shilajit they are using). I do not like Dabur, i.p. since they started broadcasting the commercials emphasizing the aphrodisiac powers of Shilajit with half naked ladies and such - I find this to be in very poor taste. The addition of lead to Shilajit tablets had them banned in Canada, recently.