There are many different origins of "sand" some is predominately calcium from sea shells and coral, some is SiO
2 [quartz], some AlO
2, some volcanic glass, etc. and all combinations of these. Sand is particulate with grains often between 0,1 and 2,0 millimeters (coarser than this and it is called gravel finer and it is silt) there should not be much very fine [ < 0,01 mm] grains.
Wikipedia says:
Sand feels gritty when rubbed between the fingers (silt, by comparison, feels like flour).
The composition of sand is highly variable, depending on the local rock sources and conditions. The bright white sands found in tropical and subtropical coastal settings are eroded limestone and may contain coral and shellfragments in addition to other organic or organically derived fragmental material.
[2] The gypsum sand dunes of theWhite Sands National Monument in New Mexico are famous for their bright, white color. Arkose is a sand orsandstone with considerable feldspar content, derived from the weathering and erosion of a (usually nearby) graniticrock outcrop. Some sands contain magnetite, chlorite, glauconite or gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basaltic (lava) with a high olivine content. Many sands, especially those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color.