| Which of the three modes of rock origin - igneous, metamorphic, and sedimentary - can form rocks with crystalline texture? | All three can form rocks with crystalline texture. However, igneous and sedimentary don't always. What other textures can they have? Under what circumstances? |
| Which of the three modes of rock origin - igneous, metamorphic, and sedimentary - can form rocks with clastic texture? | Sedimentary. (There are exceptions. For example, volcanic ash consists mostly of glass fragments. When the fragments accumulate, they may be welded or cemented together to form a rock with clastic texture. One could debate whether such a rock should be considered igneous or sedimentary.) |
| Which of the three modes of rock origin - igneous, metamorphic, and sedimentary - can form rocks with glass texture? | Igneous. |
| Here we have grains surrounded by a cement. How might the differences in grain size be explained?
| HINT: How is grain size related to duration and length of sediment transport? |
| What transportation/depositional processes or conditions result in sediment that is well sorted?
| HINT: Compare sediment transported and deposited by streams, landslides and glacial ice. |
| What transportation/depositional processes or conditions result in sediment that is poorly sorted to unsorted? | HINT: Compare sediment transported and deposited by streams, landslides and glacial ice. |
| What transportation/depositional processes or conditions result in sediment that is graded? | HINT: Compare sediment transported and deposited by streams, landslides and glacial ice. |
| How do distance and duration of transport affect angularity of sediment grains? | HINT: As sediment is transported, the particles may strike and rub against each other. |
| Here we have interlocking grains or no grains (glass). For rock textures with interlocking grains, how might the difference in grain size be explained? Frame your answer in terms of three formational environments (environments in which crystallization/precipitation took place): (a) solutions (b) melts (c) solids.
| - Solutions: HINT: How do cooling rates and rates of evaporation affect grain size? In what geologic environment (igneous, sedimentary or metamorphic) might cooling and evaporation occur?
- Melts: HINT: How does cooling rate affect grain size? In what geologic environment (igneous, sedimentary or metamorphic) might such cooling occur? In nature, what factors might affect the rate of cooling of a melt?
- Solids: HINT: How does heating and cooling a solid (without melting it) affect grain size? In what geologic environment (igneous, sedimentary or metamorphic) might such changes occur?
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| How may the presence of glass be explained? | HINT: Does glass form from a solution, a melt or a solid? In what geologic environment (igneous, sedimentary or metamorphic) might glass form. What does glass indicate about rate of cooling? |
| Describe a situation in nature where a melt begins to cool at one rate and then is placed in a new situation where the rate of cooling increases, and eventually results in a crystalline solid that has two distinct grain sizes. | HINT:  |
| Does grain shape serve to distinguish between crystalline igneous, sedimentary and metamorphic rocks? | Well-formed crystals can form in all three types of rocks. |
| What kind of information might grain shape provide for crystalline rocks? | HINT: What relationship may there be between shape and (a) rate of cooling and (b) early vs. late crystallization? |
| Under what circumstances does glass, with or without vesicular texture, form in nature? | HINT: Where is the rate of cooling sufficiently rapid for glass to form? |
| Where, specifically, is vesicular glass rather than non-vesicular glass likely to occur? | HINT: See the location of vesicular and non-vesicular glass within a lava flow. |
| Briefly describe one or more natural environments in which the material out of which a rock is made may develop an oriented texture due to deposition. Is the environment igneous, sedimentary, or metamorphic? | HINT: Under what circumstances does sediment settle out through still water? |
| Briefly describe one or more natural environments in which the material out of which a rock is made may develop an oriented texture due to shaking and compaction. Is the environment igneous, sedimentary, or metamorphic? | HINT: Under what circumstances does sediment accumulate under agitated circumstances. |
| Briefly describe one or more natural environments in which the material out of which a rock is made may develop an oriented texture due to compression and rotation. Is the environment igneous, sedimentary, or metamorphic? | HINT: |
| Briefly describe one or more natural environments in which the material out of which a rock is made may develop an oriented texture due to compression and selective growth. Is the environment igneous, sedimentary, or metamorphic? | HINT: |
| Briefly describe one or more natural environments in which the material out of which a rock is made may develop an oriented texture due to flow. Is the environment igneous, sedimentary, or metamorphic? | HINT: Under what circumstances might mineral grains be transported in a fluid? Think volcanoes and streams. |