Mineral Twins - PowerPoint PPT Presentation

1 / 13
About This Presentation
Title:

Mineral Twins

Description:

Swallowtail. Baveno. Manebach. Polysynthetic. Cyclic. Marcasite. Carlsbad Twin ... Swallowtail Twin. Two monoclinic minerals form a V-shape. Selenite. Baveno Twin ... – PowerPoint PPT presentation

Number of Views:130
Avg rating:3.0/5.0
Slides: 14
Provided by: tra74
Category:

less

Transcript and Presenter's Notes

Title: Mineral Twins


1
Mineral Twins
Contact Twin
2
Twin Definitions
  • Twin Rational intergrowth of two or more single
    crystals of the same mineral
  • Twin Law Describes a twin relationship
    including axis, center or plane and type of twin
  • Twinning Formation of a twin

3
Twin Definitions con.
  • Twin Axis Plane of rotation such that one
    crystal may be rotated 180 to become concordant
    with another
  • Twin Plane Plane around which components of a
    twin (crystals) are arranged symmetrically or
    reflected

4
Two General Twin Types
  • Contact
  • Two parts are joined along a common plane
  • Penetration
  • Two or more parts of the crystals appear to
    penetrate into each other

5
Common Twin Types
  • Carlsbad
  • Japan
  • Swallowtail
  • Baveno
  • Manebach
  • Polysynthetic
  • Cyclic

Marcasite
6
Carlsbad Twin
  • Produced by 2-fold rotation on the c-axis

7
Japan (Law) Twin
  • Crystals form at right angles to each other

8
Swallowtail Twin
  • Two monoclinic minerals form a V-shape

Selenite
9
Baveno Twin
  • Produced by reflection on 021

orthoclase
10
Manebach Twin
  • Produced by reflection on 001

microcline
11
Polysynthetic Twin
  • Repeated twinning of three or more individuals
    according to the same twin law
  • Common in plagioclase

12
Cyclical Twin
  • Composition surfaces are not parallel
  • Rutile (rutile star), chrysoberyl, cassiterite

Rutile
Chrysoberyl
13
Thin Section Twinning
  • Tartan Twinning (Pericline Law)
  • Orthoclase, microcline
  • Albite Twinning (Polysynthetic)
  • Plagioclase
Write a Comment
User Comments (0)
About PowerShow.com