VARIATIONS IN NANOMETER-SCALE FEATURES AND CRYSTAL MORPHOLOGY IN CALCIUM CARBONATE PRECIPITATES

This research explores the relationship between calcium carbonate and organic compounds. The objective was to create carefully controlled precipitates in the lab and use them to identify similar structures found in nature in rocks and other precipitates. The hypothesis tested was that organic compounds would influence the morphology of crystals in the early stages of precipitation.

Separate sterilized beakers containing calcium carbonate and sterile water were placed in an Air Clean hood with different organic compounds (palmitic acid and urease in separate beakers) for 12, 24, 48, 72 and 96 hour durations to allow the growth of CaCO₃ crystals.

After 12 hours, samples containing palmitic acid showed 2-micron long fuzzy dumbbells. After 24 hours, control samples showed rhombohedral calcite crystals and abundant spherical proto crystals; samples containing urease showed inter-grown rhombohedral calcite and acicular aragonite needles, composed of nanometer-scale spherical structures, sometimes dendritically branched, forming fan shapes or large botryoidal mineral shapes. After 48 hours, one control sample showed smooth surfaces on rhombohedral crystals with no visible proto crystals. Samples containing palmitic acid showed rhombohedral crystals and abundant irregular textures unlike any mineral. One sample containing urease showed clusters of rhombohedral structures coated in organic material. One 72-hour and one 96-hour control sample showed abundant proto crystals collected into rhombohedral-shaped clusters.

The images created show some textures similar to those found in natural environments in hot springs and from the Caribbean. A greater understanding of the relationship between organic compounds and CaCO₃ precipitates has potential applications in many industries, medicine, and the search for extra terrestrial life.