sandstone classification by pettijohn, sample point counting, framework grain composition, ternary diagram

1. Classification of sandstone
By Himangshu Saikia

2. Contents
● Classification
● Pettijohn classification
● Point counting
● Ternary diagram

3. Informal names -
● Micaceous sandstone
● Calcareous sandstone and
● Ferruginous sandstone
Sandstone Classification

4. ● Diligent petrographic analysis and point-counting of terrigenous
sands and sandstones demonstrated that the dominant
framework grain types are quartz, feldspar and lithic fragments
(QFL).
● Today, the popular classification schemes incorporate these
three components in triangular QFL plots , originally constructed
by R.H.Dott and later modified by Pettijohn, Potter and Siever, .

5. Pettijohn’s
classification

6. The Pettijohn
classification of
sandstones, often
referred to as a
‘Toblerone plot’

8. Arkose with K-feldspar (pinkish-
orangish) and quartz (gray)
grains
Arkose is generally formed from the
weathering of feldspar-rich igneous
or metamorphic, most commonly
granitic, rocks, which are primarily
composed of quartz and feldspar

9. Quartz Arenite

10. Lithic arenite

11. Point counting
Sandstone classification
is typically determined
by identifying mineral
composition at 300
equally spaced points
across a thin-section.

12. Sample Point
Count
Composition at 300 points is identified. The relative abundance of framework grains
to matrix determines whether the rock is an arenite, a wacke, or a mudstone. The
framework composition is normalized to determine type of arenite or wacke.

13. Ternary Diagrams
The normalized
framework percentages
are plotted on ternary
diagrams to determine
rock composition.

15. Thank you