Educational worksheet for learning about igneous rocks, including identification and classification based on texture and formation.

You’re working on “Igneous Rocks Worksheet #2” — a standard Earth Science exercise that tests your understanding of igneous rock classification based on texture, mineral composition, and cooling history.

Since I can’t see the image you uploaded, I’ll solve the worksheet *based on the text you provided*, which includes:

- 11 short-answer questions
- A table to fill in using an “Earth Science Reference Tables”

Let’s go step by step.

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## ✔ PART 1: Short Answer Questions

1. Name four felsic igneous rocks.

> Answer: Rhyolite, Granite, Obsidian, Pumice
> *(Felsic = rich in silica, light-colored minerals like quartz & feldspar)*

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2. Name four mafic igneous rocks.

> Answer: Basalt, Gabbro, Andesite (sometimes considered intermediate), Diorite (also intermediate — but often grouped with mafic in simplified curricula)
> *Better precise answer*: Basalt, Gabbro, Peridotite, Diabase
> *(Mafic = rich in magnesium & iron, dark-colored minerals like olivine & pyroxene)*

> 💡 Note: In many middle/high school curricula, Basalt, Gabbro, Andesite, and Diorite are accepted — even though Andesite/Diorite are technically intermediate. For strict accuracy: Basalt, Gabbro, Peridotite, and Komatiite (but Komatiite is rare). Stick with Basalt, Gabbro, and two others if needed — perhaps include Scoria or Dunite if allowed.

> 📌 Simplified classroom answer: Basalt, Gabbro, Andesite, Diorite

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3. Name a plutonic, mafic igneous rock.

> Answer: Gabbro
> *(Plutonic = formed underground, slow cooling → coarse-grained. Mafic = dark, iron/magnesium-rich. Gabbro fits both.)*

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4. Which igneous rock cooled slowly under ground and contains mostly quartz and potassium feldspar?

> Answer: Granite
> *(Slow cooling → plutonic → coarse-grained. Quartz + K-feldspar = felsic → granite is the classic example.)*

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5. As igneous rocks become more mafic, they also become (color)?

> Answer: Darker
> *(Mafic minerals like olivine, pyroxene, amphibole are dark green/black. Felsic = light white/pink. So as rocks get more mafic, color darkens.)*

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6. As igneous rocks become more felsic, they also become (density)?

> Answer: Less dense
> *(Felsic minerals like quartz and feldspar are lighter in weight/density than mafic minerals like olivine. So felsic rocks = lower density.)*

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7. Which igneous rock is fine-grained and has a lot of pyroclastic material?

> Answer: Pumice
> *(Fine-grained = rapid cooling. Pyroclastic = volcanic fragments. Pumice is frothy, glassy, full of bubbles from gas escape during eruption — classic pyroclastic rock.)*

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8. Name a coarse-grained igneous rock composed mainly of olivine.

> Answer: Peridotite
> *(Coarse-grained = plutonic. Mainly olivine = very mafic. Peridotite is the ultramafic rock dominated by olivine.)*
> ⚠️ *Note: Not listed in your table — but it’s the correct geological answer. If you must pick from the table, none fit perfectly — but Gabbro may contain some olivine. Still, Peridotite is best.*

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9. Name an intrusive, dense and dark-colored igneous rock.

> Answer: Gabbro
> *(Intrusive = plutonic = slow-cooled. Dense & dark = mafic. Gabbro is the textbook example.)*

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10. Igneous rocks are classified mainly by their:

> Answer: Texture and Composition (or Mineral Content)
> *(Texture = grain size → tells us cooling rate. Composition = felsic/mafic → tells us mineral content. These are the two main classification criteria.)*

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11. One can determine where an igneous rock formed by observing the:

> Answer: Grain size (texture)
> *(Large crystals = slow cooling = underground (intrusive/plutonic). Small/no crystals = fast cooling = surface (extrusive/volcanic).)*

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## ✔ PART 2: Fill in the Table Using Earth Science Reference Tables

You’re given this table:

| Rock | Formed from... | Cooling rate | Crystal size | Texture |
|-----------|----------------|--------------|--------------|-------------|
| Rhyolite | Lava | Slow | Small | Coarse |
| Basalt | | | | Fine |
| Gabbro | | | | |
| Pumice | Lava | Fast | No crystals | |
| Obsidian | | Very fast | | Glassy |
| Granite | Magma | | Large | |

> ⚠️ Some entries in your table are incorrect — likely placed there to test your knowledge. Let’s fix them using standard Earth Science Reference Tables (like those used in NY State Regents or similar curricula).

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🔍 Corrected & Completed Table:

| Rock | Formed from... | Cooling rate | Crystal size | Texture |
|-----------|----------------|--------------|--------------|-------------|
| Rhyolite | Lava | Fast | Small | Fine |
| Basalt | Lava | Fast | Small | Fine |
| Gabbro | Magma | Slow | Large | Coarse |
| Pumice | Lava | Fast | No crystals | Glassy / Frothy |
| Obsidian | Lava | Very fast | No crystals | Glassy |
| Granite | Magma | Slow | Large | Coarse |

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🧠 Explanation of Corrections:

- Rhyolite: Extrusive (lava), cools fast → small crystals → fine texture. *Your table said “slow” and “coarse” — that’s wrong. That’s granite.*
- Basalt: Extrusive (lava), fast cooling → fine texture, small crystals.
- Gabbro: Intrusive (magma), slow cooling → large crystals → coarse texture.
- Pumice: Extrusive, very fast cooling with gas → no crystals → glassy/frothy texture.
- Obsidian: Extrusive, extremely fast cooling → no crystals → glassy.
- Granite: Intrusive (magma), slow cooling → large crystals → coarse texture.

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## ✔ FINAL ANSWERS SUMMARY

Short Answers:

1. Rhyolite, Granite, Obsidian, Pumice
2. Basalt, Gabbro, Andesite, Diorite *(or Basalt, Gabbro, Peridotite, Diabase for stricter accuracy)*
3. Gabbro
4. Granite
5. Darker
6. Less dense
7. Pumice
8. Peridotite
9. Gabbro
10. Texture and composition
11. Grain size (texture)

Table (Corrected):

| Rock | Formed from... | Cooling rate | Crystal size | Texture |
|-----------|----------------|--------------|--------------|-------------|
| Rhyolite | Lava | Fast | Small | Fine |
| Basalt | Lava | Fast | Small | Fine |
| Gabbro | Magma | Slow | Large | Coarse |
| Pumice | Lava | Fast | No crystals | Glassy/Frothy |
| Obsidian | Lava | Very fast | No crystals | Glassy |
| Granite | Magma | Slow | Large | Coarse |

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✔ You’ve now completed the worksheet accurately! Let me know if you’d like a printable version or flashcards for review.