Limestone

Physical Properties

Hardness: 3 (Mohs scale); Color: cream, tan, or yellowish-brown; Luster: dull to earthy; Texture: clastic or non-clastic grain structure; Cleavage: none in rock form, rhombohedral in calcite crystals; Specific Gravity: 2.3-2.7

Formation & Geological History

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from calcium-rich waters in caves or springs.

Uses & Applications

Extensively used in construction as building stone, road base, and a key ingredient in cement/concrete. Also used as a soil conditioner and in the production of lime.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most cave systems in the world are formed in limestone because it is easily dissolved by acidic groundwater.

Field Identification & Locations

Identify in the field by testing with a drop of cold dilute hydrochloric acid; it will effervesce (fizz) vigorously. It is commonly found in ancient seabed deposits and mountainous regions.

Identified on: 4/15/2026

Mode: Standard