Why The Silver Block White But The Silver Powder Black?

Silver Powder is white shiny, face-centered cubic metal, the CAS No. is 7440-22-4, and it is soft, ductile second only to gold, is an excellent conductor of heat and electricity. Silver Powder does not react with water and atmospheric oxygen, and turns into ozone, hydrogen sulfide and sulfur. It is inert to most acids and can dissolve quickly in dilute nitric acid and hot concentrated sulfuric acid. 

Hydrochloric acid can corrode its surface and dissolve in molten alkali hydroxide, peroxide base and cyanide base in the presence of air or oxygen. Most silver salts are sensitive to light and are insoluble in many acids.

Why the silver block is white is that it reflects the partially absorbed light, and thus the color of the complementary light.

The surface of the silver powder is unevenly distributed, and the volume of the powder is small, making it difficult to reflect light. The light is absorbed, but it is not reversed, so it shows the black.

This is the same as the iron powder is black, and the iron block has a metallic luster.