Tankan (Sudh)

English Name



Tankan is Borax mineral (Na2B4O7, 10 H2O), also known as Tincal.


Samskrta : Tankanaka, Tanga, Tanka, Saubhagya

Regional Name

Bangali - Sohaga, English - Borax, Tincal, Gujarati - Tankana Khara, Khadiyo Khara, Hindi - Suhāga, Kannad - Biligāra, Belgar, Malayalam - Pongaaram, Marathi - Tanka´a Khara, Punjabi - Sohaga, Tamil - Venkaram (S.F.I.), Telugu - Veligaram, Urdu - Tankar, Suhaga (N.F.U.M.)

Broad Classification

Borax (Sodium borate)

Origin and occurrence:

Tankan occurs as deposits from volcanic emanations (fumaroles), hot springs and in dried up shallow basins (Playa) or saline lakes. It occurs mostly in the waters of various saline lakes in the salt deposits that have been formed through evaporation of such lakes. The origin of Tankan involves simple concentration and evaporation, which is accompanied by some chemical and mineralogical transformations to give rise toTankan (borax). An evaporite mineral, it occurs associated with halites, sulphates, carbonates and other borates like ulexite and colemanite. Economically workable deposits of Tankan  are not yet discovered in India, and the domestic need is met by imports of crude borates, which are refined to produce ¯a¬ka´a and boric acid. Small quantity of Tankan since early times, however, was being obtained from salt lakes in Leh district of Jammu and Kashmir and Tibet, where it occurs today also. Non-exploitable occurrences of Tankan are known in Surendranagar district in Gujarat and Jaipur and Nagaur districts in Rajasthan.

Physical Properties

Nature : Crystalline lumps, Colour : White, Streak : White, Cleavage : Poor, Fracture : Conchoidal, Lustre : Vitreous, Tenacity : Brittle, Transparency : Translucent, Hardness : 2 to 2.5, Sp. Gr. : 1.65 to 1.7, Taste : Sweetish alkaline

Optical Properties

Biaxial, Negative, with ηα, 1.447, ηβ, 1.469 and ηγ, 1.472 (Appendix-2)

Chemical Properties:

Effect of Heat: 
  • Heated on a burner flame using blowpipe, ¯a¬ka´a bubbles up and fuses to a clear glassy bead.
  • It colours the flame yellow due to sodium and when moistened with sulphuric acid and alcohol, gives a green flame due to boron (Appendix-3.4.3).
Reaction with acids:
  • With hydrochloric acid - gives yellow colour solution in cold condition and on boiling dissolves completely.
  • With sulphuric acid - gives colourless solution in cold condition and on boiling dissolves completely.
Solubility in water: Tankan is completely soluble in purified water producing an alkaline solution as tested by a red litmus paper turning blue. Assay:
  • Tankan should contain not less than 35% B2O3 (Boron trioxide) (Appendix-3.2.14).
  • Tankan should contain not less than 15% Sodium (Na) (Appendix-3.2.13).
Heavy metals and Arsenic: Tankan should not contain more than the stated limits for the following: - Arsenic = 5 ppm and Cadmium = 4 ppm (Appendix-3.2). Śodhana Shall not be used in formulations without subjecting it to śodhana.

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