TY - JOUR

T1 - Twinning of Tetrahedrite-OD Approach

AU - Makovicky, Emil

PY - 2021

Y1 - 2021

N2 - The common twinning of tetrahedrite and tennantite can be described as an order-disorder (OD) phenomenon. The unit OD layer is a one-tetrahedron-thick (111) layer composed of six-member rings of tetrahedra, with gaps between them filled with Sb(As) coordination pyramids and triangular-coordinated (Cu, Ag). The stacking sequence of six-member rings is ABCABC, which can also be expressed as a sequence of three consecutive tetrahedron configurations, named alpha, beta, and gamma. When the orientation of component tetrahedra is uniform, the alpha, beta, gamma, alpha sequence builds the familiar cage structure of tetrahedrite. However, when the tetrahedra of the beta layer are rotated by 180 degrees against those in the underlying alpha configurations and/or when a rotated alpha configuration follows after the beta configuration (instead of gamma), twinning is generated. If repeated, this could generate the ABAB sequence which would modify the structure considerably. If the rest of the structure grows as a regular cubic tetrahedrite structure, the single occurrence of the described defect sequences creates a twin.

AB - The common twinning of tetrahedrite and tennantite can be described as an order-disorder (OD) phenomenon. The unit OD layer is a one-tetrahedron-thick (111) layer composed of six-member rings of tetrahedra, with gaps between them filled with Sb(As) coordination pyramids and triangular-coordinated (Cu, Ag). The stacking sequence of six-member rings is ABCABC, which can also be expressed as a sequence of three consecutive tetrahedron configurations, named alpha, beta, and gamma. When the orientation of component tetrahedra is uniform, the alpha, beta, gamma, alpha sequence builds the familiar cage structure of tetrahedrite. However, when the tetrahedra of the beta layer are rotated by 180 degrees against those in the underlying alpha configurations and/or when a rotated alpha configuration follows after the beta configuration (instead of gamma), twinning is generated. If repeated, this could generate the ABAB sequence which would modify the structure considerably. If the rest of the structure grows as a regular cubic tetrahedrite structure, the single occurrence of the described defect sequences creates a twin.

KW - tetrahedrite

KW - tennantite

KW - twinning

KW - order&#8211

KW - disorder approach

KW - tetrahedral framework

U2 - 10.3390/min11020170

DO - 10.3390/min11020170

M3 - Journal article

VL - 11

JO - Minerals

JF - Minerals

SN - 2075-163X

IS - 2

M1 - 170

ER -