Calcite

specimen number:
2013616

location:
Ben Hogan Quarry, Black Rock, Arkansas, USA

description:
A loose glassy gemmy sharply twinned calcite crystal with no matrix. Quite unusual and rare for this locality and species, this is in excellent condition.

The Ben Hogan Quarry, located near Black Rock in Lawrence County, Arkansas, is a prominent limestone and dolostone operation situated within the Ozark Plateaus province. Geologically, the quarry extracts material from the Ordovician-aged Plattin and Kimmswick Limestones, which are part of a thick sequence of carbonate rocks deposited in a shallow epicontinental sea. These formations are known for their high calcium content and occasional vugs containing secondary minerals such as calcite, dolomite, and quartz. Historically, the quarry has served as a vital source of aggregate and industrial stone for the region for several decades, with significant production activity continuing into the present day. While primarily an industrial site, it is recognized by mineral collectors for producing well-crystallized specimens, particularly various forms of calcite that occur within the fractured limestone beds.

Twinning in calcite is a common crystallographic phenomenon where two or more crystals grow together in a symmetrical manner according to specific geometric laws. This occurs most frequently along four distinct planes, with twinning on the {01-12} plane, often called the rhombohedral twin, being the most prevalent and frequently caused by mechanical stress or pressure. Another notable form is twinning on the {0001} plane, known as the basal twin, or the {10-11} plane, which can result in heart-shaped or butterfly twins that are highly sought after by collectors. These twins form as a result of a change in the crystal lattice orientation during growth or due to external physical deformation, allowing the calcite to accommodate internal strain or specific environmental conditions.

Questions about this specimen?
Send an email or call us: 314-341-1811.