Well, we haven't done analysis at an asteroid, so it is somewhat speculative, but we can use as a starting point the pieces that have landed on earth-meteorites.<br />There are two broad common groups of minerals.<br /><br />Silicates and Irons.<br /><br />Stony meteorites are Pyroxenes, Silicates with varying amounts of Iron, Magnesium, and Calcium.<br />Chodrites and Pallasites are mostly Olivine, a Silicate with varying amounts of Iron and Magnesium.<br />Carbonaceus chondrites are a class of water bearing silicates with varying amounts of Iron and Magnesium.<br />Quartz in very rare.<br />Nickel Iron is common, alloys of Iron Nickel and Cobalt.<br />Iron Sulphide is present in stony-iron meteoroites, Magnetite in Carbonaceus chondrites<br /><br />A small part of chondrites are types of Feldspar, an aluminum Silicate with varying amounts of sodium and calcium.<br /><br />THe proportions in asteroids are rather speculative, except on those that are large enough to have differentiated, where like the earth, the Iron-Nickel has sunk to the core.<br /><br />Here on earth, about 70% are stony, 30% are Irons, with a small percentage of Stony-Irons. However some of that is a selection effect, since Irons are much easier to spot (rather unearthlike, see the NJ meteorite story in SS&A), the actual proportion derived from observed falls is /> 90% stony meteorites, hence Irons are rare.<br /><br />Water? Unknown. Purely speculative at this point.<br />Other ices, ditto.<br /><br />Of course, there is no sharp dividing line between comets and asteroids, so many asteroids probably do have ices, except those that regularly (very short period) visit inside 2 AU or so, which are probably depleted.<br /><br />The source on these compositions is Norton's <font color="yellow">"Rocks from Space" </font>/safety_wrapper> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>