Rock salt, the mineral halite, is mined from exposed layers in cliff faces, road cuts and cave walls with a pick and chisel, then crushed, dissolved, filtered and recrystallised to purify it. It can be used raw for hides, livestock and other non-food jobs, but salt for people should come from a deposit you know is clean, because rock salt can carry clay, gypsum, additives from earlier use and, in industrial or road stockpiles, chemicals that are not food-safe.
Part of Salt Production & Sourcing
Rock salt is the sodium chloride mineral halite found in underground and exposed beds, left by ancient seas that evaporated, and mined directly rather than made by evaporation.
What To Look For
Halite occurs as layers (beds) or as larger masses (domes), and sometimes appears at the surface where erosion has cut into it, as in cliff faces, road cuts or cave walls, as the parent describes. In dry climates it can also form crusts in dried lake beds. It looks like grey, white or translucent crystalline rock that tastes salty. Rock salt is often interlayered with clay and gypsum, which shows as grey, red or white bands.
The chemistry article on mineral deposits explains field recognition of salt among the other raw minerals (Mineral Deposits).
Mining And Preparing
The parent’s method is simple: identify exposed layers, cut with a pick and chisel, crush, dissolve in water, filter and recrystallise. The parent adds that rock salt for preservation need not be food-grade pure. That is acceptable for uses where purity does not matter, such as preserving hides or as livestock salt (subject to the livestock needs in Iodine and mineral supplementation). For food, treat the claim carefully: “where it came from” decides whether it is fit to eat. Salt from an untouched natural bed is a different thing from salt in a bag of unknown origin, a road or de-icing stockpile, or a deposit contaminated by past industry; those can carry additives, anticaking agents or metals.
Test a deposit before relying on it.
- Taste: clean halite is simply salty; a bitter taste means magnesium salts.
- Dissolve a weighed piece, filter, and weigh the residue to find how much is clay and gypsum.
- Know the surroundings: mines, oil seeps, industrial sites or old waste upstream.
What You Need
- Pick, chisel, hammer and a bucket or sled to carry
- Eye protection and a cloth mask against salt chips and dust
- A crusher or pounding stone and a hard flat surface to break the rock on
- Water, cloth filters, and a pan for the purification steps (Removing impurities and bitter minerals)
Method: Take Rock Salt From A Surface Deposit
Step 1: Choose a stable exposed face. Look for overhangs and loose blocks above.
Step 2: Work from the bottom up only where the face is stable. Prefer to take blocks that have already fallen.
Step 3: Cut slabs with a chisel and bring them down in pieces you can carry.
Step 4: Crush, dissolve, filter and recrystallise for food use.
Step 5: Keep rock salt of known source separate from salt of unknown origin.
Common Mistakes
- Treating “rock salt” as food salt without asking where it came from.
- Undercutting a face. A salt overhang can fall without warning.
- Mining deep without ventilation. See the safety block.
Safety
Falls, dust, and enclosed spaces
Salt faces and cave roofs can collapse, and cutting under them kills. Do not tunnel or work inside caves without shoring and ventilation, because enclosed workings can hold bad air, including oxygen-poor air and, near some deposits, gas. Work in daylight with a second person outside. Salt dust irritates eyes and lungs. Flooding is a risk wherever fresh water meets salt: brine can seep into workings quickly.
What’s Next
- Learn next: Removing impurities and bitter minerals — turning crude salt into food salt
- Combine with: Salt springs and licks — the other inland route