Which substance is found in the dried-up lakes of Tibet and California?

Tincal, commonly known as natural borax, is a hydrated sodium borate mineral with the chemical formula Na₂B₄O₇·10H₂O. It occurs naturally in evaporite deposits, particularly in regions with a history of volcanic activity or arid climates where water from boron-rich hot springs evaporates, leaving behind crystalline borax layers. Notably, tincal is found in the dried-up lakes of Tibet and California, especially in areas like Death Valley and the Borax Lake region.

This mineral is one of the most important natural sources of boron. Boron does not occur freely in nature but is found combined in minerals such as borax (tincal), colemanite (Ca₂B₆O₁₁·5H₂O), and kernite (Na₂B₄O₆·5H₂O). Among these, tincal is easily soluble in water, which makes it commercially valuable for boron extraction and industrial applications.

When borax is heated, it loses water molecules and forms sodium metaborate (NaBO₂) and boric anhydride (B₂O₃), compounds essential in glass, enamel, and ceramic industries. It is also used in the manufacture of detergents, welding fluxes, and laboratory reagents.

The geological origin of tincal is linked to evaporative concentration of boron-rich lake waters over thousands of years. In regions such as Tibet and California, periodic evaporation of shallow borate lakes under dry conditions caused precipitation of borax crystals along the lake beds, leading to the formation of vast natural deposits.

Chemically, tincal plays a crucial role in inorganic chemistry as it demonstrates the formation of borates and their behavior upon heating. Its study helps students understand hydration, dehydration, and complex salt formation.

Therefore, Tincal (Na₂B₄O₇·10H₂O) is the correct answer, as it is the natural borax found in the dried-up lakes of Tibet and California, serving as a key mineral source of boron in nature.