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Related Concept Videos

Sulfur Assimilation01:20

Sulfur Assimilation

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Sulfur is an essential element in biological systems, contributing to synthesizing key biomolecules, including amino acids such as cysteine and methionine, and cofactors such as coenzyme A and biotin. Microorganisms primarily assimilate sulfur as sulfate (SO₄²⁻) from the environment, which must undergo a series of biochemical transformations before it can be incorporated into cellular components. As sulfate is highly oxidized, it must undergo assimilatory sulfate reduction to...
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Preparation and Reactions of Sulfides02:26

Preparation and Reactions of Sulfides

5.0K
Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.
5.0K
Precipitation and Co-precipitation01:17

Precipitation and Co-precipitation

1.9K
Precipitation and coprecipitation methods can be used to separate a mixture of ions in a solution. In qualitative inorganic analysis, ions that form sparingly soluble precipitates with the same reagent are separated based on the differences in solubility products. For example, consider the separation of Cu(II) and Fe(II) ions by precipitation as insoluble sulfides. First, copper(II) sulfide is precipitated by the addition of acidic H2S, where the dissociation of H2S is suppressed. Adding H2S...
1.9K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

1.1K
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
1.1K
Ionic Crystal Structures02:42

Ionic Crystal Structures

14.5K
Ionic crystals consist of two or more different kinds of ions that usually have different sizes. The packing of these ions into a crystal structure is more complex than the packing of metal atoms that are the same size.
Most monatomic ions behave as charged spheres, and their attraction for ions of opposite charge is the same in every direction. Consequently, stable structures for ionic compounds result (1) when ions of one charge are surrounded by as many ions as possible of the opposite...
14.5K
Alkali Metals03:06

Alkali Metals

19.7K
Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the alkali metals are unusually low for metals and decrease going down the group, while the density increases going down the group with the exception of potassium (Table 1).
Table 1: Properties of the alkali metals
19.7K

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Preparation of Authigenic Pyrite from Methane-bearing Sediments for In Situ Sulfur Isotope Analysis Using SIMS
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Pyrite contact twins.

Yves Moëlo1, Massimo Nespolo2, François Farges3

  • 1Nantes University, CNRS, Institut des Matériaux Jean Rouxel, IMN, Nantes, F-44000, France.

Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials
|February 7, 2023
PubMed
Summary
This summary is machine-generated.

This study details two new contact twins in Peruvian pyrite, revealing complex crystallographic relationships. The findings challenge previous interpretations of spinel twins in pyrite, linking their occurrence to structural pseudo-symmetry.

Keywords:
contact twiniron cross twinmerohedrymorphologypyritereticular merohedryspinel twin

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Area of Science:

  • Mineralogy
  • Crystallography
  • Geology

Background:

  • Contact twins in pyrite are rare and their formation mechanisms are not fully understood.
  • Previous literature on pyrite twins, such as spinel twins, requires re-evaluation based on new observations.

Purpose of the Study:

  • To describe and analyze two novel examples of contact twins in pyrite from Peru.
  • To clarify the crystallographic operations and composition planes involved in these twins.
  • To reassess the interpretation of known pyrite twins, particularly spinel twins, in light of new data.

Main Methods:

  • Morphological analysis of pyrite crystals.
  • Determination of crystallographic forms, twin operations, and composition planes.
  • Comparison with existing literature and theoretical crystallographic principles.

Main Results:

  • Description of two distinct contact twins in Peruvian pyrite, one lenticular and the other V-shaped.
  • Identification of specific crystallographic forms ({120}, {111}, {100}), twin operations (⟨110⟩ rotation, reflection), and composition planes ((111), (110)).
  • Reinterpretation of a previously described spinel twin as a rotation twin with a 180° rotation about ⟨211⟩ axes.

Conclusions:

  • The occurrence of these complex pyrite twins is directly related to the pseudo-symmetry of crystallographic orbits.
  • The study provides a more accurate understanding of twinning in pyrite.
  • Revises the classification of certain pyrite twins, emphasizing precise crystallographic analysis.