Image credit: Scott Brande
Identification and Classification
We will observe and evaluate unknown rock samples to identify them by name, according to a classification.
Identification and classification are not the same thing.
- classification - an arrangement of relationships among categories based upon similarities and differences, e.g., conglomerate is a sedimentary rock composed of rounded, gravel-sized (larger than 2 mm) fragments
- identification - a process of assigning an object to a previously named group or category, e.g., "this particular rock sample is a conglomerate because I can see the sample is composed of rounded, gravel-sized (larger than 2 mm) fragments
There are numerous classifications of sedimentary rock that serve different purposes (e.g., used by experts, industry, students). A simplified classification of sedimentary rock is included here for the purpose of learning how to observe features important in distinguishing some of the more common sedimentary rock and assigning a name to an unknown sample.
Video Introduction to Sedimentary Rock Classification
Watch this short video for an introduction to a simplified classification of the common sedimentary rocks.
Classification of Common Sedimentary Rock
Nature's production over time of mineral matter and its change through weathering is prodigious and widespread. A consequence of the heterogeneous composition of the planet is a bewildering diversity of chemical compounds and weathered fragments in sedimentary rock.
The simplified classification table presented below focuses on features that may be observable without additional equipment (e.g., no hand-lenses, thin-sections, polarizing microscopes). As noted before, an advantage of digital online media is that images and video may be processed (e.g., zoomed) to partially substitute for the lack of hand lenses and low power microscopes.
Click image to enlarge.