Minerals crystallization sequence

The tube-in-tube experiment is a very powerful method to determine the sequence of precipitation of secondary minerals as function of temperature for a chosen chemical system. Chemical reactions occur quickly (within 40 days) and the transport by diffusion of chemical elements is efficient. Similar crystallization sequences are observed in both experiments, suggesting that the transitions between the different mineral phases are not only controlled by the composition of the solution but also by temperature. The experimental design does not strictly correspond to the geometry encountered at the Soultz-sous-Forets site and therefore needs to... 

The primary minerals crystallize from high-temperature melts (magma), often under conditions of high pressure beneath the earth s crust. The sequence of crystallization of the common minerals in forming igneous rocks is called the Bowen reaction series. As diagrammed in Figure 6.1, it is seen that there are actually two reaction series ... 

Table 13.7. Crystallization sequence (Rosenbuch) Early minerals Apatite, Zircon, Titanite...

Lanthanide-concentrating minerals can also be selective, depending on which lanthanides more readily substitute into their structures. The true extent of their selectivity is less easily inferred from compositons of natural minerals than for the lanthanide minerals proper. Their lanthanide abundances tend to reflect those of their parent liquids, which are usually not known. Those minerals that do not show a consistent pattern of domination by light lanthanides, heavy lanthanides, or even middle lanthanides are usually listed as complex. Presumably, whatever selectivity they have is insufficient to overcome variations in composition caused by variations in parent liquid composition. Because many of these minerals form late in a crystallization sequence, the lanthanide distributions of their parents may differ considerably from those of the original magmas or those of the rocks in which the minerals occur. 

Vermicuhte is an expandable 2 1 mineral like smectite, but vermiculite has a negative charge imbalance of 0.6—0.9 per 02q(0H)2 compared to smectite which has ca 0.3—0.6 per 02q(0H)2. The charge imbalance of vermiculite is satisfied by incorporating cations in two water layers as part of its crystal stmcture (144). Vermiculite, which can be either trioctahedral or dioctahedral, often forms from alteration of mica and can be viewed as an intermediate between UHte and smectite. Also, vermiculite is an end member in a compositional sequence involving chlorite (37). Vermiculite may be viewed as a mica that has lost part of its K+, or a chlorite that has lost its interlayer, and must balance its charge with hydrated cations. 

The rapid oxidation of Fe " close to the surface and in the presence of a fair supply of organic matter and dissolved Si, conditions which hinder crystallization, leads to ferrihydrite instead of goethite. The ferrihydrite is, however, often associated with goethite and it is still unknown whether the two minerals have formed simultaneously or in sequence. Simultaneous formation seems more likely for two reasons in the first place, low-temperature hydrolysis of Fe " or oxidation of Fe ", both, led to mixtures of the two oxides in different proportions if the rate of hydrolysis/oxidation was varied (Schwertmann et al. 1999 Schwertmann Cornell, 2000). Secondly, the transformation of ferrihydrite, especially in the presence of Si, appears to be extremely sluggish. 

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