Glauconite is a clay mineral that occurs in the form of dark green granules in many marine sands. The granules are more or less equal in size to the particles of the sand matrix in which they occur. However, because glauconite consists of clay minerals, it is much softer than the silica sand. Glauconite granules are therefore easy to deform and shatter. This has an important impact on the geotechnical properties and behaviour of sandy soils with a significant level of glauconite. Mechanical operations on sands containing glauconite and which cause the glauconite granules to shatter, such as drilling tunnels, compaction and piling, can cause a lot of problems. The behaviour of the soil gradually turns from sandy to significantly clayey, and therefore requires different working methods. Because the pore water in sands containing glauconite always contain iron, special precautions are required when lowering groundwater and reversing dewatering operations. This article provides an overview of the nature and geotechnical properties of sands containing glauconite and devotes specific attention to the shattering effect. Practical issues that may arise when working in such sands are also looked at in depth.