Grossmanite
Chemical formula: Ca(Ti<sup>3+</sup>,Mg,Ti<sup>4+</sup>)AlSiO<sub>6</sub>
Grossmanite is a rare, dark brown mineral from the pyroxene group, discovered in the Allende meteorite, named after Professor Lawrence Grossman.
Properties
- Mohs hardness
- 6
- Luster
- Vitreous
- Density
- 3.68
- Cleavage
- Good on {110}
- Fracture
- Uneven
- Transparency
- Translucent to Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of grossmanite is impossible without advanced analytical techniques. Due to the microscopic size of the grains, it requires the use of an electron microprobe (for chemical composition analysis) and X-ray diffraction or electron backscatter diffraction (EBSD) to confirm the crystal structure. In an electron microscope image, it appears as dark grains within lighter minerals in CAI inclusions. ## Distinguishing from Similar Minerals Under a microscope, grossmanite is practically indistinguishable from other titanium-rich pyroxenes, such as esseneite or davisite. Definitive differentiation is possible only based on precise chemical analysis, which shows the dominance of trivalent titanium (Ti³⁺) in a specific structural position. ## Crystal Forms Grossmanite forms only microscopic, subhedral (imperfectly formed) grains, often with an irregular habit. It is not observed in the form of well-developed, macroscopic crystals.
Geological environment
## Genesis Grossmanite is a mineral of extraterrestrial origin. It forms under conditions of high temperature and very low oxygen partial pressure, characteristic of the early solar nebula. It crystallizes as one of the primary components of calcium-aluminum-rich inclusions (CAIs) in carbonaceous chondrites, mainly of the CV3 type. ## Mineral Associations This mineral co-occurs with other minerals typical of CAIs in the Allende meteorite. It is most often associated with spinel, melilite (åkermanite-gehlenite), hibonite, perovskite, and other pyroxenes, such as diopside and titanium-rich augite (fassaite). ## Localities The only confirmed locality for grossmanite is the Allende meteorite, which fell in Chihuahua, Mexico, in 1969. This is the type locality for this mineral.
Rarity
Extremely rare
For collectors
## Quality Criteria Grossmanite does not occur in the form of collector's specimens in the traditional sense. Its value is purely scientific. For research institutions and specialized meteorite collectors, the most valuable items are thin sections (polished mounts) of the Allende meteorite in which the presence of grossmanite within CAI inclusions has been identified and documented. The quality of such a preparation depends on the clarity of the structures and the quality of the analyses, not on the appearance of the mineral itself.
Care and storage
## Cleaning Specimens containing grossmanite (usually meteorite fragments) should not be wet-cleaned, especially with water or chemicals. Any contaminants should be removed only mechanically, dry, using a soft brush or compressed air. ## What to Avoid Water, detergents, and chemical agents can damage both grossmanite itself and the surrounding meteorite matrix. High humidity, which can lead to the oxidation of associated minerals (e.g., iron sulfides), should be avoided. Sudden temperature changes should also be avoided. ## Storage Meteorite fragments containing grossmanite should be stored under stable conditions, preferably in a dry environment. It is recommended to use sealed containers (so-called "membrane boxes") or cabinets with controlled humidity, with the addition of a desiccant (e.g., silica gel).