Limestone (specifically Crushed Limestone/Calcictic)

Physical Properties

Hardness: 3 on Mohs scale; Color: White to light grey with tan/yellow iron staining; Luster: Dull/Earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (not visible in mass); Specific Gravity: 2.7

Formation & Geological History

Formed in warm, shallow marine waters through the accumulation of shell, coral, algal, and fecal debris. This specimen likely originates from the Phanerozoic eon deposits commonly used for industrial gravel.

Uses & Applications

Primary use in construction as road base, concrete aggregate, and railroad ballast. Also used in the production of cement, lime for soil stabilization, and as an industrial filler.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. It is the primary source of the world's commercial lime and is essential for the steel-making process.

Field Identification & Locations

Identify in the field by its softness (can be scratched by a steel nail) and its vigorous effervescence (fizzing) when reacting with dilute hydrochloric acid or strong vinegar. It is commonly found in quarries worldwide.

Identified on: 4/25/2026

Mode: Standard