oxide group of minerals

1. OXIDES
Presented
by
BITIHOTRA NAYAK
Roll No. 418AG2013
Department of Earth & Atmospheric Science
6th Nov. 2018

2. Talk Outlines
 Introduction
 Classification of Oxides
 Chemical Formula & Structure
 Physical & Optical properties
 Occurrences

3. INTRODUCTION
 Oxygen combines directly with one or more metallic cations to form an oxide.
E.g. Hematite, Rutile, Spinel etc.
 All of these minerals (except ice) are isodesmic (all the bonds are of same strength).
 The bonding in oxide minerals is dominantly ionic.
 Most of the oxides have high order of symmetry.
 Structures are usually based on a systematic packing of oxygen ions, often in cubic
or hexagonal close packing.
 Cations occupy tetrahedral and octahedral sites between the regularly packed
anions.
 The oxide minerals (except ice) are found as accessory minerals in igneous,
metamorphic & sedimentary rocks.

4. CLASSIFICATION
MINERAL COMPOSITION
X2O Cuprite
Ice
Cu2O
H2O
XO Periclase
Zincite
MgO
ZnO
XY2O4 Magnetite
Chromite
Spinel
Chrysoberyl
FeFe2O4
FeCr2O4
MgAl2O4
BeAl2O4
X2O3 Hematite
Corundum
Ilmenite
Fe2O3
Al2O3
FeTiO3
XO2 Rutile
Cassiterite
Pyrolusite
Uranite
TiO2
SnO2
MnO2
UO2
X,Y = Metal Cation, O = Oxygen

5. X2O Group
 Chemical composition - Cu2O
 Crystal system – Isometric
 Structure – Body-centred cube in which Oxygen anions occupy the
corners and centre of the unit cell, Cu occupies four of the eight
octants.
Cu
O
O
O
O
O
Cu
Cu
Cu
CUPRITE
Fig. Structure of cuprite

6.  PHYSICAL PROPERTIES
 Colour – Various shades of Red
 Streak – Brownish red
 Lustre – Submetallic
 Transparency – Opaque
 Cleavage – Poor (111)
 Fracture - Conchoidal
 Hardness - 3.5 – 4
 Specific Gravity – 5.9 – 6.1
 OPTICAL PROPERTIES
 Interference colour – Bluish grey olive green
 Isotropism – Anisotropic
 Birefringence – Very weak
 Relief – high (+) ve
 Refractive index – High
 Occurrences – Near-surface oxidized portion of copper-bearing
hydrothermal sulfide deposits.
Fig. Hand specimen of Cuprite

7. XO Group
 Formula – ZnO
 System – Hexagonal
 PHYSICAL PROPERTIES
 Colour – Orange to deep red
 Streak – Orangish yellow
 Lustre – Sub-adamantine
 Cleavage – Perfect (100)
 Hardness – 4
 Specific Gravity – 5.6
 OPTICAL PROPERTIES
 Uniaxial (+) ve
 Pinkish brown colour
ZINCITE
Fig. Hand specimen of Zincite

8. PERICLASE
 Formula – MgO
 System – Isometric
 PHYSICAL PROPERTIES
 Colour – Colourless or white
 Streak – White
 Lustre – Vitreous
 Cleavage – Perfect (100)
 Hardness – 5.5
 Specific Gravity – 3.58
 OPTICAL PROPERTIES
 Isotropic
 Colourless
Fig. Hand specimen of Periclase

9. XY2O4 Group
 Formula – MgAl2O4
 System – Isometric
 Structure – Cubic close-packed oxygen
with X and Y cations in tetrahedral and
octahedral coordination sites among the
oxygen anions.
SPINEL
Fig. Structure of Spinel

10.  PHYSICAL PROPERTIES
 Colour – Red, brown, blue
 Streak – White
 Lustre – Vitreous
 Transparency – Transparent to
translucent
 Cleavage – None
 Fracture - Conchoidal
 Hardness – 8
 Specific Gravity – 3.5-4
 OPTICAL PROPERTIES
 Isotropic
Fig. Hand specimen of Spinel

11. MAGNETITE
 Formula – FeFe2O4
 System – Isometric
 Structure – Same as spinel structure
Fig. Hand specimen and structure of Magnetite

12.  PHYSICAL PROPERTIES
 Colour – Black
 Streak – Black
 Lustre – Metallic
 Transparency – Opaque
 Cleavage – None
 Fracture – Sub-conchoidal
 Hardness – 6
 Twinning – Twinning on (111) (spinel twin) is common
 Specific Gravity – 5.2
 OPTICAL PROPERTIES
 Opaque
 Isotropic in thin section

13. CHROMITE
 Formula – FeCr2O4
 System – Isometric
 Structure – same as Spinel.
Fig. Hand specimen of Chromite

14.  PHYSICAL PROPERTIES
 Colour – Black
 Streak – Brown
 Lustre – Metallic
 Transparency – Opaque
 Cleavage – None
 Fracture – Sub-conchoidal
 Hardness – 6
 Twinning – Twinning on (111)
 Specific Gravity – 5.1
 OPTICAL PROPERTIES
 Opaque
 Isotropic in thin section

15. X2O3 Group
 Formula – Fe2O3
 System – Hexagonal (Trigonal)
 Structure – Hexagonal close-packed oxygen anions, with metal cations
occupying octahedral sites between the anions
X O
HEMATITE
Fig. Hand specimen and structure of Hematite

16.  PHYSICAL PROPERTIES
 Colour – Steel grey, red-brown to black
 Streak – Cherry red
 Lustre – Metallic
 Transparency – Opaque
 Cleavage – None
 Fracture – Sub-conchoidal
 Hardness – 5.5-6.5
 Twinning – Twinning on {001} & {101}
 Specific Gravity – 4.9-5.3
 OPTICAL PROPERTIES
 Opaque
 Uniaxial (-) ve
 Alteration – may be altered to iron oxide minerals.

17.  Formula – Al2O3
 System – Hexagonal (Rhombohedral)
 Structure – Hexagonal close-packed oxygen anions, with metal
cations occupying octahedral sites between the anions.
CORUNDUM
Fig. Hand specimens of corundum

18.  PHYSICAL PROPERTIES
 Colour – Blue, Red, Brown
 Streak – White
 Lustre – Adamantine
 Transparency – Transparent to translucent
 Cleavage – None
 Fracture - Uneven
 Hardness – 9
 Twinning – Simple twins on {101}
 Specific Gravity – 3.9-4.1
 OPTICAL PROPERTIES
 Colourless
 Uniaxial (–) ve
 High relief
 Low birefringence

19.  Occurrence and associations
 Occurs as an accessory mineral in metamorphosed carbonates
and sediments, in some Al-rich igneous rocks, and in placers.
 Varieties .
 Sapphire (typically blue) and Ruby (red) are gem varieties
of corundum.

20. XO2 Group
 Formula – TiO2
 System – Tetragonal
 Structure – Distorted TiO6 octahedra share edges to form chains.
Chains are connected by corner-sharing octahedra. Each O is in
triangular coordination, bonded to three Ti.
Fig. Hand specimens of Rutile
RUTILE

21. Rutile and Cassiterite structure

22.  PHYSICAL PROPERTIES
 Colour – Reddish Brown to black
 Streak – Pale to light brown
 Lustre – Adamantine
 Transparency – Transparent to translucent
 Cleavage – Good prismatic {100} and {110}
 Fracture – Sub-conchoidal
 Hardness – 6-6.5
 Twinning – Simple twins on {101}
 Specific Gravity – 4.24
 OPTICAL PROPERTIES
 Deep Red in thin section
 Uniaxial (+) ve
 High relief
 High birefringence

23. CASSITERITE
 Formula – SnO2
 System – Tetragonal
 Structure – Distorted SnO6 share edges to form chains. Chains are
connected by corner-sharing octahedra. Each O is in triangular
coordination, bonded to three Sn.
Fig. Hand specimen of Casiterite

24.  PHYSICAL PROPERTIES
 Colour – Brown to black
 Streak – white
 Lustre – Metallic
 Transparency – Transparent to translucent
 Cleavage – Good {100} and poor {111}
 Fracture – Sub-conchoidal
 Hardness – 6-7
 Twinning – Simple twins on {101}
 Specific Gravity – 7
 OPTICAL PROPERTIES
 Yellow, brown, red in thin section
 Uniaxial +Ve
 High relief
 High birefringence

25. 1) Klein, Hurlbut. Manual of Mineral Science
2) Perkins. Mineralogy
3) Nesse W.D. Introduction to Mineralogy
4) Wikipedia
5) Figures from Internet
REFERENCES

26. THANK YOU