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Factors Affecting the Growth Rate of Crystals

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Author: Janice VanCleave

What You Need to Know

Stalactites are rock structures that hang from the roof of a cave. Stalagmites are rock structures that stick up from the floor of a cave and are directly under stalactites. The sheetlike, layered deposits on the walls or floors of caves are called flowstones. A column is a vertical structure that forms when a stalactite and a stalagmite join together. Limestone is a rock made of calcium carbonate. Calcite is a type of crystal made of calcium carbonate.

How Do Stalactites and Stalagmites Work?

A stalactite is a long, icicle-shaped structure that hangs from the roof of a cave. Stalactites form when rainwater containing carbon dioxide from the air combines with limestone. As this liquid mixture percolates through the roof of a cave, some of it falls to the cave floor below, some wets the ceiling of the cave, and some dissolves the limestone. When the water evaporates small particles of calcium carbonate, generally in the form of calcite, are left clinging to the ceiling. Over a long period of time, the calcite deposit builds up, eventually forming a stalactite. Drops of mineral-rich liquid that fall from the end of a stalactite produce a mound of calcite projecting up from the cave floor, forming a stalagmite. When the stalactite and the stalagmite touch, a column is formed. The mineral-rich liquid that runs down the walls of the cave produces layer upon layer of calcite that hardens to form flowstone.

How Do Stalactites and Stalagmites Work?

Fun Fact

One way to remember which cave crystals hang down from the ceiling (stalactites) and which grow up from the ground (stalagmites) is: "stalactite" has a C for ceiling and "stalagmite" has a G for ground.

What Does This Have to Do with the Growth Rate of Crystals?

Because of the amount of dripping water in a cave, the humidity in the cave is high. Does humidity affect crystal growth? What about temperature? Caves are cool. At a lower temperature, water evaporates slower. Does the evaporation rate affect crystal growth?

Real-Life Science Challenge

Different kinds of crystals are always needed for new technological devices such as computers and cellular phones. Crystal growth is also studied in the medical field. For example, by modeling the crystal formation of kidney stones, scientists can better understand how these crystals aggregate (cluster together) and attach to kidney cells. This research not only will provide important information that may prove useful for preventing kidney stone disease but also for other related diseases that are caused by similar crystal formation.

Experiment

Now, start experimenting with factors that affect the growth rate of crystals.

Hints

  • Solutes that form crystals by water evaporation include table salt found at the grocery store, and Epsom salts and alum found at the pharmacy.
  • Temperature can be increased using sunlight or decreased by placing experiment materials in a refrigerator.
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