John and Sarah are doing an experiment to find out if crystal size in igneous ro

Question

John and Sarah are doing an experiment to find out if crystal size in igneous rocks can be related to the speed of cooling a magma/lava. They did not have equipment to melt rock, so they used thymol to model pieces of rock. Thymol melts easily at low temperature on a hot plate, and it cools and recrystallizes quickly. Thymol is a transparent, crystalline organic substance derived from the herb, thyme, and is used in antiseptics and disinfectants. It is not toxic, but does give off a very strong pungent odor that can irritate skin and eyes and cause headaches. Therefore. John and Sarah used a spoon to handle the thymol and did all of their work under a fume hood with supervision from their teacher. Sarah placed some thymol in a small Pyrex beaker and melted it completely under a fume hood to model the formation of magma. John pouted one half of the molten thymol into a cold Petri dish and the other half into a hot Petri dish of the same size. The results of John and Sarah's experiment are shown below. Notice that the images are enlarged. Beside each image below, measure and record the actual size range of the crystals (in mm) that formed. Igneous rocks that are made of crystals too small to see with your naked eyes or hand lens are said to have an aphoristic texture (from the Greek word for invisible). Those made of visible crystals are said to have a parotitic texture (crystals -1-10 mm) or pegmatitic texture (crystals greater than 1 cm). Which of these three igneous rock textures probably represents the most rapid cooling of mag ma/lava? REFLECT & DISCUSS This rock has a "porphyritic texture, " which means that it contains two sizes of crystals. The large white plagioclase crystals are called phenocrysts and six in a green-gray "Groundmass" of more abundant, smaller (aphanitic) crystals. Based on your work above, explain how this texture may have formed (more than one answer is possible). In your collection of numbered igneous rock samples, record the sample numbers with these textures:

Explanation / Answer

A) Molten thymol that cools in 1 minute lead to the development of numerous crystals which are smaller in size and not easily distinguishable and it’s size is less than 1 mm in size where as the liquid that cools in 3 minutes grows well and it’s size of the crystals are in the range of 1-10 mm.

B) Rapid cooling are represented by the aphanitic texture because due to the rapid cooling numerous crystallizing point’s are developed but none of them have grown well due to the rapid drop in the temperature of the liquid.

C) This type of crystallization took place with the gradual drop in the temperature and the crystalls got enough time to grow well from the liquid lava which derived it’s nutrients from the lava.

Related Questions

Navigate

• Browse (All)
• Browse J
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.