Chondrules and Their Origins

Houston, Texas: Lunar and Planetary Institute, 1983. E1 - A hardcover book in good condition that has some bumped corners and dents, lightly cocked, wrinkling on the spine edges, some scattered scartches, rubbing, scuffing, and bubbling on the cover, lightly moisture soiled, lgiht discoloration and shelf wear with no dust jacket. 9.75"x6.75", 377 pages. Satisfaction Guaranteed. A chondrule (from Ancient Greek chondros, grain) is a round grain found in a chondrite. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids. Because chondrites represent one of the oldest solid materials within the Solar System and are believed to be the building blocks of the planetary system, it follows that an understanding of the formation of chondrules is important to understand the initial development of the planetary system. Most chondrules are composed primarily of the silicate minerals olivine and pyroxene, surrounded by feldspathic material that may either be glassy or crystalline. Small amounts of other minerals are often present, including Fe sulfide (troilite), metallic Fe-Ni, oxides such as chromite, and phosphates such as merrillite. Less common types of chondrules may be dominantly composed of feldspathic material (again either glassy or crystalline), silica, or metallic Fe-Ni and sulfides. Chondrules display a wide variety of textures, which can be seen when the chondrule is sliced open and polished. Some show textural evidence for extremely rapid cooling from a molten or nearly completely molten state. Pyroxene-rich chondrules that contain extremely fine-grained, swirling masses of fibrous crystals only a few micrometers in size or smaller are called cryptocrystalline chondrules. When the pyroxene fibers are coarser, they may appear to radiate from a single nucleation site on the surface, forming a radial or excentroradial texture. Olivine-rich chondrules may contain parallel plates of that mineral, surrounded by a continuous shell of olivine and containing feldspathic glass between the plates; these are known as barred textures. Other observed textural features that are clearly the result of very rapid cooling are dendritic and hopper-shaped olivine grains, and chondrules that are composed entirely of glass. More commonly, chondrules display what is known as a porphyritic texture. In these, grains of olivine and/or pyroxene are equidimensional and sometimes euhedral. They are named on the basis of the dominant mineral, i.e. porphyritic olivine (PO), porphyritic pyroxene (PP), and porphyritic olivine-pyroxene (POP). It seems likely that these chondrules cooled more slowly than those with radial or barred textures, however they still may have solidified in a matter of hours. The composition of olivine and pyroxene in chondrules varies widely, although the range is usually narrow within any single chondrule. Some chondrules contain very little iron oxide (FeO), resulting in olivine and pyroxene that are close to forsterite (Mg2SiO4) and enstatite (MgSiO3) in composition. These are commonly called Type I chondrules by scientists, and often contain large amounts of metallic Fe. Other chondrules formed under more oxidizing conditions and contain olivine and pyroxene with large amounts of FeO (e.g., olivine with the formula (Mg,Fe)2SiO4). Such chondrules are called Type II. Most chondrites contain both Type I and Type II chondrules mixed together, including those with both porphyritic and nonporphyritic textures, although there are exceptions to this. . Hardcover. Good/No Jacket. 8vo - over 7¾" - 9¾" tall.