Sorry if some of the language is kinda haughty, I just like pretty words when talking about science.

Kran were created through divine magic, by the hand of Talad. This is known for fact. However, not all existing Kran were created that day. (As people can choose it as a race, therefore the number of Kran in existance is not limited.) So.. That means that Kran must have some way to reproduce, or that Talad creates more of them. This does, however, seem a strange task, just creating Kran out of the blue every once in awhile. If the Kran are simply magically animated constructs, as so many would have us believe, then they would not be able to reproduce, as the magic that is believed to make them move while holding their shape, think, live, and whatnot would have to be cast on their young to make them more than a stone. I was thinking, that maybe if they were enchanted, that if their young were of the same enchanted stone, then they would live too, but that just doesn\'t make sense. If that were the case, Kran could shapeshift, create things out of their bodies, only losing body mass, (such as weapons) and could not be harmed, because they would be little more than flexible rocks, held together and manipulated by magic. I believe that there is something more.
In order to maintain their existance, I believe that, even though they were created by magic, they were created with a functional system.
They would likely breathe, not Oxygen, but Carbon. When monoatomic Carbon comes in contact with SiO2, they react to produce pure Silicon, and Carbon monoxide.(SiO2 + 2C --> Si + 2CO) Which would explain a source of silicon to grow and heal, straight from their food. Breathe in Carbon Dioxide, and breathe out Carbon monoxide and Oxygen. This is however, only possible if the Kran stomach is able to break molecular bonds. A crop of sorts, to break apart the Carbon Dioxide into monoatomic Carbon, and diatomic Oxygen. The Oxygen is by far the heavier of the two, (being two atoms, each heavier than a Carbon atom) so the Carbon would ..float, as it were, to be absorbed from the top of the organ, while the Oxygen is pushed to the bottom, (assuming this organ is a vacuum aside from what has been introduced) to be absorbed and exhaled. The absorbed Carbon, would then go to the stomach to aid in digestion, which would produce Carbon monoxide, and Silicon, along with solid waste.
As for muscles, I do not see why joints could not be pushed, in the stead of pulled, by metals supersensitive to heat, which expand when electral current passes through them. (the opposite of muscles, but the same result.) And then slowly cool, and contract when current is no longer applied. (The metal muscle thing was stated before, by someone else, but in fewer words.)
I do not, however, believe that Kran have any need for blood. Comming in, I thought it would be a suspension of silicon and other things in water, but the more I thought about it, the more it made sense that substances absorb through poors inside the Kran\'s body, as opposed to traveling in a liquid.
I do realize that there are holes in this, probably rather big ones.. But hey, I\'m just doing my part in this wonderful discussion!

/me loves picking fantasy apart to think of how it should work.