Here are some descriptions of common mineral additives available to improve garden soil.

Gypsum: Light-colored, finely powdered rocks or pellets containing calcium sulfate. 

Gypsum has been used since the days of the early Greeks. It improves water penetration (drainage) and aeration for packed-down and clayey soils by making the fine particles of clay stick together and neutralizing the salt in high-sodium soils without raising the pH as lime does. The process is a chemical one, whereby sodium ions are exchanged for calcium ions, which separates the clay particles enough to create “pore space” for air and water. Because it is a neutral salt, gypsum may be used where you want to increase soil calcium without raising the pH. 

I use a handful with every tomato plant as a deterrent to blossom-end rot. It adds not only calcium but also sulfur, both secondary nutrients. It comes in a pelletized form that is easier to use than the powder form.

Lime: Also known as ground limestone, agricultural lime and garden lime. The chemical name for lime is calcium carbonate. It may be bagged as a fine white powder, granules and most commonly as pellets.

When mixed with magnesium (which is quite common) it is called dolomite or dolomitic lime. Most articles recommend dolomitic lime to be used for your lawn and garden, but today it hardly matters. Hydrated or “slaked” lime, the caustic, concentrated, dangerous-to-handle version of lime intended to be used in mortar and plaster, is not commonly available in garden centers or nurseries anymore, so there is little cause for concern.

Lime is primarily used to raise the soil pH, to make it more alkaline, or “sweeter.” Lime neutralizes soil acidity so that microorganisms can help break down organic matter into humus, but it is useful in many other ways as well. It is not considered a fertilizer, but it helps in the release of nutrients and improves the structure of clay soils by increasing moisture retention and drainage. Lime also helps control club root, a disease found in plants of the cabbage family, and tends to prevent moss growth.

Most lawns in our area need to be limed annually, and in acid soils, liming is necessary to grow many perennials and vegetables. Always depend upon an actual soil test to determine how much (if any) to apply. My own garden in Lafayette Hill has a pH of 7.1, just on the sweet side of neutral, and has never required lime. But this is not normally the case in our area.

Greensand: A pulverized rock powder, also known as glauconite. 

Greensand is mined naturally from marine deposits found near the New Jersey coast. It was called “granite dust” years ago. But it has many trace minerals and is a natural source of potash, which is great for adding potassium to vegetable garden soil. Greensand retards soil compaction and holds moisture. It is often recommended for roses and greenhouse potting mixtures where moisture retention and drainage are issues.

Epsom salts: A white powder, magnesium sulfate, containing almost 10 percent magnesium and 15 percent sulfur. Epsom salts are a good source of magnesium when a soil test indicates it is needed, although lawns that require magnesium will usually get it more quickly with an application of lime. Epsom salts get their name from a mineral spring in Epsom, England, where they were first collected.

Perlite: A light, hard, porous, gritty material that looks like tiny white balls, formed when lava (volcanic rock) is heated to a high temperature, which causes it to expand. Perlite is nontoxic, sterile and odorless; a common component of soil-less potting medium, it can be used as a rooting medium on its own. It increases drainage, improves aeration and decreases the weight of potting mixes. It also helps to retain water, which attaches to the surface of the perlite particles. 

Vermiculite: An extremely lightweight, granular substance with grains about 1/16 of an inch in diameter formed when mica chips are heated to a high temperature and expanded — actually, popped like popcorn! Vermiculate contains some potassium, magnesium and calcium, which are slowly released in soil. It is commonly used in soil mixes to increase water and fertilizer retention, as well as to lighten and open it up. It is also used as a soil amendment for vegetable containers and beds and for starting seeds. Avoid adding it to very clayey soils, as the clay bonds with the vermiculite, instead of the vermiculite breaking up the clay.