Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Wulfenite, transparent or subtranslucent mineral, consisting of lead molybdate, PbMoO4, and crystallizing in the tetragonal system (see Crystal). It was named in honor of the Austrian botanist and mineralogist Franz Xaver von Wulfen. It has a hardness of 2.75 to 3 and a specific gravity of 6.7 to 7; it shines with a vitreous to diamondlike luster. The color of the mineral ranges from yellow, orange, red, and gray, to white, most specimens being streaked with white. Wulfenite, also known as yellow lead ore, occurs chiefly in the oxidized portions of lead veins, together with such minerals as vanadinite and pyromorphite.