Lesson Plan

permineralization Lesson Plan

Lesson Plan Image
Grade Level:
Upper Elementary: Third Grade through Fifth Grade
Lesson Duration:
90 Minutes
State Standards:
Colorado Academic Standards for Science
 3rd Grade
o LS4-1
 4th Grade
o ESS1-1
 5th Grade
o ESS2-1

Essential Question

How can wood, bones, and teeth from once-living organisms turn into rock?


Students will demonstrate the process of permineralization by using a sponge to absorb a solution of water and salt crystals. The salt crystals will fill the open spaces of the sponge & harden as the water evaporates over the course of several days.


  • Permineralization is a type of fossilization that happens when minerals transported by water fill in all the open spaces of an organism or organic tissue. Within these spaces, mineral deposits form internal casts. This process occurs when water carrying minerals from the ground, lakes, or oceans seep into the cells of organic tissue to eventually form a cast of crystals.
    • Silicification – most common form of permineralization in which silica mineralization/replacement results in the formation of fine-grained quartz, chalcedony, and opal fill in pores.
  • Replacement of soft or hard body parts can occur when minerals precipitate out because of bacteria or changes in pH of the water solution.
  • Permineralization is useful when studying an organism’s internal structures particularly in plants such as the ancient Redwoods at Florissant Fossil Beds. Since the ancient Redwoods of this region became buried by lahars or volcanic mudflows, silica from the volcanic ash primarily precipitated out into the Redwoods’ cells.


Materials needed:

  • Synthetic sponges
  • Pitcher
  • Resealable sandwich or 1 gallon size bags (wash and reuse)
  • Sea salt and/or Epsom salt (50 g (each))
  • Water (150 mL)
  • Pre-made sponge “fossils” for demonstration
  • Small paper (“Dixie”) cups
  • Optional – Scissors


  • Check activity bin for sufficient reusable supplies: plastic bags, sponges, cups, and salt.
  • Check classroom supplies bin for needed supplies: pitcher, scissors and pencils.
  • Cut sponges into small shapes or squares, ensuring there will be enough for each student.

Lesson Hook/Preview

  • When an animal or plant dies then becomes buried, water nearby or from the ground seeps through bones, wood, and other organic tissues. The water deposits minerals into all the open spaces or cells. Students will recreate this process using a synthetic sponge and saltwater solution. The experiment will demonstrate how salt in a water solution can form solid crystals inside the open spaces of the sponge.


  • Have students separate into small groups of 4 or 5.
  • Give brief lesson on permineralization and the purpose of this experiment. (page 2 “Lesson Hook and Background”)
  • Work with the class to answer assessment question #1.
  • Give each group a large plastic bag, a cup of salt, and enough empty cups and cut sponges for each student. Ask students question #2:
  • Have students describe their sponges and make notes for question #3.
  • Have one student in each group pour full cup of salt Epsom salt into a plastic zippered bag.
  • Have each student place their own sponge into the bag with the salt.
  • Carefully add water into the bag with the Epsom salt and sponges until the bag is approximately 1/4 full. Have students seal the bag shut.
  • Students will gently stir/shake the zipped bag until the Epsom salt dissolves into the water. **REMIND STUDENTS** that being too rough with the bag will destroy the fossils!
  • Once salt is dissolved and sponges have all fully absorbed solution, have students carefully remove their sponges. They will place their sponges in their own paper cup.
  • Have students describe their sponges now for question #4 and make notes.
  • While students are taking notes, use an empty paper cup to scoop a small amount of salt solution out of the bag and add to each of the cups with students’ sponges.
  • Leave sponge and saltwater filled cups out in the open air for several days to dry and crystalize.
  • Have students make a hypothesis as to what the sponges will look like and feel like in a certain number of days. Written as a statement for question #5.
  • Introduce the pre-made sponge fossils and allow students to explore and describe them. Give time to make notes, use hand lenses, and answer question #6.
  • Give a brief lesson on how the Redwoods of Florissant became permineralized. Allow discussion of how their experiment replicates this process with question #7.
Students will finish the experiment after several days of drying.


  • Fossilization
  • Permineralization
  • Replacement
  • Mineral –a naturally occurring, inorganic solid, has a well-defined chemical composition and crystal structure
  • Solution
  • Precipitate
  • Cast

Assessment Materials

Permineralization Assessment

  1. Describe the conditions required for an organism to become permineralized.
  2. What does each item in the experiment represent in the fossilization process?
  3. What does your sponge feel like? For example: is it soft, squishy, sharp…or? Describe the sponge as if you were taking a picture with words.
  4. Describe your sponge again after soaking it in saltwater. How has it changed?
  5. Using your knowledge of how permineralization happens, make a hypothesis about how the sponges will change over the next few days.
  6. Where did the salt crystals in the sponge go? How did this change the sponge’s texture and appearance?
  7. How did our sponge experiment demonstrate how the Florissant Redwood trees were fossilized?

Rubric/Answer Key

  1. Rapid burial of an organism, presence of minerals and water, sealed off from oxygen and bacteria
  2. Sponge: organism to be fossilized/petrified
Salt: minerals that will come out of solution to make crystals inside the organism bodyWater: substance that mixes with dissolved mineral to make a solution Plastic bag: an environment that has been sealed off from oxygen so that the organism cannot rot
  1. Students’ descriptions of the sponge pre-experiment will vary.
  2. Students’ descriptions of the sponge post-experiment will vary but should include descriptions of minimal change but that they are not identical.
  3. Hypothesis examples: The saltwater solution will evaporate over time leaving salt crystals inside the open spaces o the sponge. Or The saltwater solution will change the appearance and texture of the sponge as the water evaporates. (Many options will be correct! Remind students that their hypothesis cannot really be “wrong’—it leads to more science!)
  4. Salt crystals dissolved into the water allowing the salt to fit into all the empty spaces of the sponge where water can also go. This action had made the sponge hard, sharp, sparkly…etc. Crystals can be seen inside the sponge and have filled in some of the smallest holes.
  5. The salt represents the silica that came from the volcanic ash and dissolved in the groundwater. The trees, even though they are much larger than a sponge, still soaked up the mineral water and allowed silica crystals to form inside the cells and empty spaces of the tree.

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Last updated: September 10, 2022