Return to course homepage.
 

pseudomorph - a mineral that has been replaced by another, but whose original shape has been maintained.  Pseudomorphs are common in aqueously altered chondrites.

CV subgroups - The CVox (Allende) and CVox (Bali) subgroups mentioned by Brearley are equivalent to the CV_oxA and CV_oxB subgroups we learned about earlier.

framboidal - a microscopic aggregate of grains, often occurring in spheroidal clusters.  This type of texture is often observed for magnetite in heavily altered chondrites.

MAI (Mineralogical Alteration Index) - a scheme developed by Browning et al. for CM chondrites to track progressive alteration. This scheme includes a formula to take into account three factors, including (a) alteration in the matrix of cronstedite to Mg-serpentine (increases with increasing MAI), (b) total vol% alteration (increases with increasing MAI), and (c) vol% isolated matrix silicate (decreases with increasing MAI).

del (D) - This is the ratio of heavy hydrogen (deuterium, or D) to normal H, normalized to a standard, given in per mil notation, analogous to the expression for del 18O. As we will see, large enrichments in del (D) are found in organic matter within petrologically pristine chondrites.

pH - This parameter (dimensionless) is a measure of hydrogen ion activity (effective H ion concentration) in a solution. pH = -log a(H⁺), where a(H⁺) = activity of hydrogen ion.  Lower values (<7) of pH represent progressively acidic solutions, and higher values (>7) represent progressively more basic solutions.

Eh (or eH) - This parameter (measured in volts) reflects the ability of a solution to be an electron donor or acceptor relative to a standard H₂ electrode.  Oxidizing solutions have Eh > 0 and function as electron acceptors; reducing have Eh < 0 and function as electron donors.

Vug (~1 mm across) filled with blue halite (salt) in Zag
(H-chondrite breccia). This halite probably formed
by evaporation of brines in the H-chondrite
parent body.  See this link for a short
article about extraterrestrial salt in chondritic meteorites.
From: http://www.nyrockman.com/meteorite/gallery/zag.htm
 

Transmitted light image of coarse halite in Monahans
(H-chondrite breccia); field of view ~ 1 mm wide.  Water-filled
fluid inclusions can be seen within the halite.  This halite
probably formed by evaporation of brines in the H-chondrite
parent body.
From: http://www-curator.jsc.nasa.gov/astromaterials/specialfeatures/monahans/
 

dating of alteration -  Brearley discusses short-lived chronology data for alteration, making reference to three systems: (a) decay of ²⁶Al to ²⁶Mg; (b) decay of ⁵³Mn to ⁵³Cr; and (c) decay of ¹²⁹I to ¹²⁹Xe.  As we have learned, estimates of initial ²⁶Al/²⁷Al, ⁵³Mn/⁵⁵Mn, and ¹²⁹I/¹²⁷I values (= short-lived species/stable species) can be used to estimate relative age.