The three large posters are mosaics of back-scattered electron (BSE) images made from a few dozen separate images taken with the scanning electron microscope (SEM). In BSE images, the lighter shades are denser phases of higher atomic number. In practice, this is a proxy for the element iron � white regions and light-gray regions have higher iron contents than darker gray regions. Most black areas are holes in the sample. The image on the left is that of the Semarkona LL3.0 ordinary chondrite, one of the least-altered chondritic meteorites known. This sample offers a great deal of information about the primitive materials that were accreting at very early stages of Solar-System history. The image in the middle is that of the LAP 02342 CR carbonaceous chondrite. Many of the chondrules are surrounded by white blebs (metallic iron-nickel). Almost all of the chondrules in this meteorite are darker than most of those in Semarkona; this indicates that the CR chondrules tend to have low amounts of oxidized iron. The poster on the right is of the Krymka LL3.1 ordinary chondrite. This rock is similar to Semarkona, but is slightly more metamorphosed (heated and recrystallized). Many of the chondrules seem to be aligned; this is a result of shearing in the rock induced by an impact event.