Chlorine

Chlorine is found in the Earth's crust, 0.031 % (w/w) [6], and is found naturally in:

• Gastric juice (0.05-0.1 M HCl) [3]
• Great Salt Lake, USA (4.5 M) [3]
• Salt beds (NaCl, MgCl₂, CaCl₂ [3]
• Sea water (0.54 M) [3]

The naturally occurring isotopes are ³⁵Cl (75.53 %, stable) and ³⁷Cl (24.47 %, stable) [6].