IgnRx-15
Image credit: Scott Brande
Igneous Rock A15 Resources and Instructions
Igneous Rock A15 Resources and Instructions
- Observe sample below in the image(s) and videos. Follow guided viewing questions.
- Evaluate sample for composition and texture.
- Record composition and texture observations as instructed.
- Compare features of samples to descriptions and features of igneous rock bank.
- Enter sample composition and texture on classification table (below).
- Identify the sample by name at the intersection of row (texture) and column (composition).
- Review answers and correct any errors after instructor provides answer key.
Unless otherwise noted, images and videos are by Scott Brande.
Guided Viewing Questions
Guided Viewing Questions
- Questions below guide your observation of a sample for relevant properties.
Texture
Texture
Observe the rock sample for texture. Which texture does the rock most closely resemble?
- crystalline - Does the sample exhibit visible (phaneritic) crystals? A mix of visible and microscopic crystals (porphyritic)? Just microscopic crystals (aphanitic)?
- vesicular - Does the sample exhibit holes? More rock than holes? Or, more holes than rock?
- fragmental - Does the sample exhibit a mixture of broken fragments floating in a matrix of ash? Or just fine-grained ash?
- glassy - Does the sample exhibit conchoidal fracture?
Composition
Composition
Composition is most relevant for crystalline texture.
- Are individual crystals visible - phaneritic - or invisibile - aphanitic?
- Are scattered larger crystals floating in a fine-grained (aphanitic) groundmass (matrix)?
- What is the tone (lighter or darker) of the rock?
- Is the rock more felsic (lighter tone), mafic (darker tone), or intermediate?
Refer to this simplified classification table for rock names and their properties.
Click upper right corner to pop-out table to new tab.
Whole Rock Video
Whole Rock Video
- Ruler scale below is in centimeters (subdivided into millimeters)
- Click to play YouTube video with pan-and-zoom
A15
A15
Scale in centimeters
Image credit: Scott Brande
Whole Rock View
Whole Rock View
- Ruler scale below is in centimeters (subdivided into millimeters)
- Sample typically less than 5 cm in size
- Click image to pop-out in new tab
Close-up View
Close-up View
- Enlarged view for observation of detail
- Click image to pop-out in new tab