Sugar, salt, and baking soda are pure substances that are compounds. Examples of pure substances that are crystals include salt, diamond, protein crystals, and copper sulfate crystals. Depending on who you talk to, homogeneous mixtures may be considered examples of pure substances.

A solution can be separated by a physical change, such as boiling away the solvent. Substances that are combined chemically can only be separated by a chemical change. Solutions then are combinations of substances that are not chemically combined.

Saltwater is a homogeneous mixture, or a solution. Soil is composed of small pieces of a variety of materials, so it is a heterogeneous mixture. Water is a substance; more specifically, because water is composed of hydrogen and oxygen, it is a compound.

Ordinary table salt is called sodium chloride. It is considered a pure substance because it has a uniform and definite composition. All samples of sodium chloride are chemically identical. Salt easily dissolves in water, but salt water cannot be classified as a pure substance because its composition can vary.

There is no such thing as pure water. The very concept of ‘pure’ water is misleading. Most water will contain certain ions, such as calcium and magnesium, even if it is just a trace amount. These minerals are the ones that define whether water is hard or soft, and they play a role in taste.

Ice, iron, hydrochloric acid, calcium oxide, mercury are pure substances as they have definite composition.

Main compounds of milk are lactose and casein. And it is also called a colloidal mixture (i.e. in which one substance of microscopically dispersed insoluble or soluble particles is suspended throughout another substance). Therefore milk is regarded as a mixture not as a pure substance.

Carbon

Diamond is a form of pure carbon (which is an element). Also, in order for diamond to be a unique element, the molecules that make it up should have a different number of protons than any other element on the periodic table. Since a diamond is made of carbon, it is really just another form of carbon.

Diamond is the only gem made of a single element: It is typically about 99.95 percent carbon. Diamond forms under high temperature and pressure conditions that exist only within a specific depth range (about 100 miles) beneath the earth’s surface.

Conclusion. Diamond is an element made of carbon and negligible amounts of impurities and elements like nitrogen. As an element, it is resistant to chemical activity. The strong tetrahedral bonds between its atoms make this gem a good conductor of heat and a poor conductor of electricity.

Carbon is a solid non-metal element. Pure carbon can exist in very different forms….Diamond and graphite.

tungsten

Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic….Is Diamond A Metal Or A Stone?

The only hardness test that will identify a diamond is scratching corundum. Corundum, which includes all rubys and sapphires, is 9 on the hardiness scale. If your suspected diamond crystal can scratch corundum, then there is a good chance that you found a diamond. But NO OTHER HARDNESS TEST will identify a diamond.

Rough diamonds don’t have any sparkle. A flawless raw diamond may be worth more than a cut diamond with a low clarity grade. Color: Most colorless (or white) diamonds have natural yellow or brown tints of color in them. The more color a diamond has, the less bright and lustrous it’ll appear.

Source: English Wikipedia. (PhysOrg.com) — Currently, diamond is regarded to be the hardest known material in the world. But by considering large compressive pressures under indenters, scientists have calculated that a material called wurtzite boron nitride (w-BN) has a greater indentation strength than diamond.

Pound for pound, diamonds are not very good at stopping bullets. The energy absorbed by diamond shattering is much less than the energy absorbed by metals deforming. A plate of steel would be better at stopping bullets than a plate of diamond.

Diamond, while much harder than the soft metal lead, is not as dense. When a lead bullet hits a target, the metal is soft enough to immediately flatten on impact or even break apart and heavy fragments may even bounce around in the target causing massive damage.