Introduction

River pebble is a kind of pure natural stone. It is taken from the sand and gravel hills which were uplifted from the ancient river bed after the crustal movement tens of millions of years ago. It is constantly squeezed and rubbed during the process of mountain torrent impact and flowing water transportation. In the course of tens of thousands of years of vicissitudes and changes, they have experienced the movement of waves and washes, lost irregular edges and corners by the impact and friction of gravel, and were buried in the ground together with the sediment for millions of years of silence. The main chemical composition of river pebble is silicon dioxide, followed by a small amount of iron oxide and trace elements and compounds such as manganese, copper, aluminum and magnesium. They have different pigments, such as red iron, blue copper, purple manganese, yellow translucent silica colloidal pith, emerald green minerals and so on. Because of the different kinds and contents of these pigment ions dissolved in silica hydrothermal solution, they show a variety of shades of color. So that the river cobbles appear black, white, yellow, red, dark green, gray and so on. Most of the pebbles are near the Haihe River. Black sand grains are gathered on the pebbles. The pebbles should account for more than half of the volume. Because of their wide distribution, common appearance and beautiful appearance, they are ideal choice for yard, road and building construction.