mineral formation

minerals under pressure

In the last several years, many incredible discoveries have been made exploring how minerals behave under high pressure, like rocks experience inside the Earth. If a mineral is placed in a special machine and then squeezed, eventually it may convert into a different mineral. Ice is a classic example of a material that undergoes solid-solid "phase transitions" as pressure and/or temperature is changed. A "phase diagram" is a graph which plots the stability of phases of a compound as a function of pressure and temperature. A phase diagram for water (ice) is included in the Figure 1.6. The phase diagram is split up into 3 main areas for the solid crystalline phase (ice), the liquid phase (water), and the gas phase (water vapor). Notice that increasing pressure lowers the freezing point and raises the boiling point of water. What does that do to the stability conditions of the liquid phase? A sample phase diagram for water. Click image to the left or use the URL below. URL:

textbook_image

minerals from salt water

When water evaporates, it leaves behind a solid precipitate of minerals, as shown in Figure 1.2. When the water in glass A evaporates, the dissolved mineral particles are left behind. Water can only hold a certain amount of dissolved minerals and salts. When the amount is too great to stay dissolved in the water, the particles come together to form mineral solids, which sink. Halite easily precipitates out of water, as does calcite. Some lakes, such as Mono Lake in California (Figure 1.3) or The Great Salt Lake in Utah, contain many mineral precipitates. Tufa towers form when calcium-rich spring water at the bottom of Mono Lake bubbles up into the alkaline lake. The tufa towers appear when lake level drops.

textbook_image

textbook_image

minerals from hot underground water

Magma heats nearby underground water, which reacts with the rocks around it to pick up dissolved particles. As the water flows through open spaces in the rock and cools, it deposits solid minerals. The mineral deposits that form when a mineral fills cracks in rocks are called veins (Figure 1.4). Quartz veins formed in this rock. When minerals are deposited in open spaces, large crystals form (Figure 1.5). Amethyst formed when large crystals grew in open spaces inside the rock. These special rocks are called geodes.

textbook_image

textbook_image

formation from magma

Imagine a rock that becomes so hot it melts. Many minerals start out in liquids that are hot enough to melt rocks. Magma is melted rock inside Earth, a molten mixture of substances that can be hotter than 1,000 C. Magma cools slowly inside Earth, which gives mineral crystals time to grow large enough to be seen clearly (Figure 1.1). Granite is rock that forms from slowly cooled magma, containing the minerals quartz (clear), plagioclase feldspar (shiny white), potassium feldspar (pink), and bi- otite (black). When magma erupts onto Earths surface, it is called lava. Lava cools much more rapidly than magma. Crystals do not have time to form and are very small. The chemical composition between minerals that form rapidly or slowly is often the same, only their size differs. Existing rocks may be heated enough so that the molecules are released from their structure and can move around. The molecules may match up with different molecules to form new minerals as the rock cools. This occurs during metamorphism, which will be discussed in the "Metamorphic Rocks" concept.

textbook_image

formation from solutions

Water on Earth, such as the water in the oceans, contains chemical elements mixed into a solution. Various processes can cause these elements to combine to form solid mineral deposits.

mineral formation

Minerals form in a variety of ways: crystallization from magma precipitation from ions in solution biological activity a change to a more stable state as in metamorphism precipitation from vapor

instructional diagrams

No diagram descriptions associated with this lesson

questions

minerals can form by

a) precipitation from ions in solution

b) crystallization from magma

c) biological activity

-->  d) all of the above

although both are made of carbon, why is diamond better than graphite for jewelry?

a) graphite has more impurities than diamond so it is an unattractive gray color.

-->  b) diamond forms at very high pressures so it is hard and attractive.

c) diamond has impurities that make it harder and more attractive than graphite.

d) diamonds are less expensive than graphite so they are more widely used in jewelry.

magma is melted rock outside of earth.

a) true

-->  b) false

volcanic rocks have small or no crystals because they are from lava that cooled slowly.

a) true

-->  b) false

as a rock is heated, in what order do the minerals melt?

a) they melt from the rock in the same order that they formed as the magma cooled.

-->  b) the first ones to melt are the last ones that formed as the magma cooled.

c) all of the minerals solidify and melt at the same time.

d) the minerals melt in random order.

as pressure on a mineral increases, the mineral may melt and then cool as a different mineral, called a phase transition.

a) true

-->  b) false

a mineral that forms when water evaporates is gold

a) gold

b) silver

-->  c) halite

d) diamond

this is a graph that plots the stability of phases of a compound as a function of pressure and temperature.

a) cartesian graph

b) line graph

c) phase transition

-->  d) phase diagram

minerals form when the concentration of ions gets too great in a fluid.

-->  a) true

b) false

minerals form from hot water in this way:

-->  a) hot water dissolves materials as it moves through the rock, but then as the water moves

b) hot water dissolves materials as it moves through the rock, but then the water evaporates and leaves behind minerals.

c) hot water contains minerals that precipitate when the water evaporates away.

d) as pressure on the hot water lowers, minerals are stable and precipitate from the water.

diagram questions

No diagram questions associated with this lesson