Yogi is a large basalt-type rock.

Matt Golombek video
Matt Golombek audio --

From there we decided we should pretty much go straight toward Yogi, which is the large, big rounded rock which is almost perched in some of the rover images. It looks like it's sitting on a point and it's a big round rock. When we got close to it, it turned out to be more difficult to get the APX up against it and we had our first fenderbender on Mars where the wheel of the rover actually went up against Yogi. But we did back off and get the APX up against it and found that that turned out to be a less silca-rich rock, more like a basalt primitive mantle melt that we kind of expected on Mars. Except that part of the surface looks like it was covered with dust and that if you subtract that dust away, then Yogi could be a higher-silca rock as well. Both of which are truly outstanding discoveries.

Joy Crisp video
Joy Crisp audio --

Yogi is a really large rock and it does have some texture in it that has some clues to what it is. It has a radiating bundle of fractures in the upper left-hand side. These cracks could be result of cooling from a melt. I've seen cracks like this in lava flows; they've also been found in welded pyroclastic flows, which are volcanic rocks which have been exploded and deposited by eruption through the air. But there are other possibilities: it's possible this could be some kind of sedimentary structure as well.

Ron Greeley video
Ron Greeley audio --
Yogi has a two-toned appearance which makes it an extremely interesting rock in terms of surface processes. One side of the rock is very reddish, crusted appearance; the other side appears to be scoured by the wind and free of that dust and weathered material. This tells us it has probably been sandblasted to remove that outer crust.