greensand

Greensand is a greenish sandstone or siltstone that derives its coloration from the mineral glauconite, a green iron potassium silicate. The assemblage typically includes quartz along with minor amounts of calcite and other minerals, giving the rock a distinct green hue and sandy to granular texture.

Geologically, greensand forms in shallow marine shelf environments where sedimentation rates are slow enough for glauconite crystals to develop and accumulate with sand-sized grains. These greensand beds occur in sedimentary sequences around the world, with ages ranging from the Cretaceous to the Eocene in many regions.

In addition to its geological interest, greensand is mined for glauconite and is widely used in horticulture as a soil amendment. It is marketed as a slow-release source of potassium and as a soil conditioner. The potassium content of greensand can vary, and the mineral is relatively insoluble compared with conventional potash fertilizers, so nutrient release to plants tends to be gradual. As a soil amendment, greensand may improve soil structure, drainage, and moisture retention, particularly in sandy soils or in organic farming systems, when used alongside other amendments.

Overall, greensand is valued for its long-term contributions to soil potassium and trace minerals rather than for rapid nutrient delivery. Its effectiveness depends on soil type, crop requirements, and how it is applied.