How to identify Fossilized Worm Tubes in Sandstone

To correctly identify Fossilized Worm Tubes in Sandstone (Trace fossil (Skolithos ichnofacies) in sandstone), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Variable, typically matching the host sandstone (e.g., white, tan, brown, reddish-brown, grey). The infill of the tubes may be slightly different in color or texture due to variations in sediment composition or diagenesis.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy, characteristic of sandstone.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Clastic, sandy. The tubes themselves will have a similar sandy texture but may feel smoother or coarser depending on the infilling sediment. The overall texture is often rough due to the quartz grains.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Not applicable, as these are trace fossils within a clastic sedimentary rock. The individual quartz grains within the sandstone are anhedral to subhedral.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Not applicable for the rock as a whole. Individual mineral grains (e.g., quartz) within the sandstone do not exhibit cleavage in hand specimen.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Shallow-marine, high-energy environments such as beaches, foreshore, shoreface, and shallow subtidal zones. These environments are characterized by strong wave and current action, leading to well-sorted sandy substrates and rapid sedimentation.

Key Facts

Hardness

Variable, typically 6.5-7 on Mohs scale (due to quartz grains in sandstone).

Specific Gravity

2.6-2.7 (typical for quartz sandstone).

Crystal System

Not applicable for the trace fossil; quartz is trigonal.

Color

Variable, depending on the host sandstone and cementing agents.

Luster

Dull to earthy.

Transparency

Opaque.

Fracture

Irregular to conchoidal (for individual quartz grains).

Cleavage

None (for the rock as a whole).

Composition

Primarily quartz (SiO2) grains, with varying amounts of feldspar, lithic fragments, and accessory minerals. The 'tubes' are simply infillings of the same or slightly different sandy sediment.

Physical characteristics

• Crystal Habit: Not applicable for the trace fossil; individual quartz grains are anhedral to subhedral.
• Cleavage Type: None.
• Fracture Type: Irregular to granular.
• Tenacity: Brittle.
• Luster Type: Dull to earthy.

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