Diamond is 100 % Carbon, atomic number 6 on the periodic table. Gold, symbol Au is atomic number 79 and is like diamond, a pure substance. Rust on the other hand is ferric oxide or Fe₂O₃. The mineral is called Hematite. It has a blood red streak. That is, if you think you have some hematite, rub the mineral on an unglazed ceramic tile (called a streak plate) and the streak is blood red.

The element in diamond is carbon (symbol C). Try and find C in the periodic table. Diamonds, particularly high quality ones, are very pure carbon. Sometimes however, small amounts of carbons neighbors in the periodic table, such as boron (symbol B), and Nitrogen (symbol N) are also found in diamond. These tend to give diamonds different colors.

Gold is an element (symbol Au). The element symbol Au comes from the Latin word for gold which is aurum. Pure gold is usually only used to store money in banks. In jewelry (which is the biggest use of gold) the gold is usually mixed with some copper (symbol Cu) to give it more strength.

Rust is usually a mixture of iron (symbol Fe) oxygen (symbol O) and some hydrogen (symbol H). Most rust has the chemical formula FeO₂H, also written as FeO (OH), and mineral name of this material is lepidocrocite (pronounced lay-pedo-kro-kite).

First, gold is an element. It is very malleable and ductile. Since pure gold is fairly soft, it is often combined with other metals to make alloys to make it a little stronger. The alloys are what you typically find in jewelry, etc.

Diamonds are made up of the element carbon. Also, graphite is also made up of carbon. The only difference between the two is the way that the atoms are bonded together.

Interestingly, graphite is the more stable form of carbon, so diamonds will eventually turn into graphite (diamonds aren't really forever!). However, this process takes thousands of years.

Rust is the common name for iron oxide, which as the name implies, is made up of the elements iron and oxygen. The compound is Fe₂O₃. Iron combines quickly with oxygen, and the process of turning iron to iron oxide is an example of corrosion.

You can see things like steel rust because steel contains iron.

The quick answer is: Diamond is a pure element, carbon; gold is a pure element, gold; and rust is a compound, Iron Oxide, of iron and Oxygen.

Diamond is pure elemental carbon, compressed to its crystal form, under extreme heat and pressure deep within the Earth. The symbol for carbon is C.

Gold is also an element, in and of itself. Its symbol is Au. It does not easily form compounds so it is found by itself, in stream beds (placer deposits) or in veins in rocks.

Rust is a compound: Iron Oxide. It is found all over; everywhere iron and oxygen come in contact! Both iron and oxygen form compounds quite easily, so they are not readily found alone. (The oxygen you breathe is O₂, not elemental oxygen.)

Rust can come in different forms, because iron (symbol Fe) normally gives up 2 or 3 electrons when it forms compounds. We call these "oxidation states." When iron gives up 2 electrons, it gets a +2 charge, and when it gives up 3 electrons, it gets a +3 charge. To make a neutral compound it must then bond with some element in the proper ratio so as to remove its "excess" positive charge (or, replace its deficit negative charge).

Oxygen (symbol O) normally takes 2 electrons when bonding with metals (including hydrogen). So, for a balanced compound of iron oxide, you have either FeO or Fe₂O₃. Here's what I mean: For FeO, you have one Fe(+2) and one O(-2) = FeO. This compound is also called Iron(II)Oxide. It is one form of rust. The charges balance like this:(+2) + (-2) = 2 - 2 = 0.

The other form of rust, Fe₂O₃, is two Fe(+3) and three O(-2), written Fe₂O₃, and also called Iron(III)Oxide. The charges balance like this:2(+3) + 3(-2) = 6 - 6 = 0.

I hope this helps. Best wishes.

Diamond is a polymorph of the element carbon (C). To give you an idea of the many uses of carbon, the macromolecules in our bodies, including DNA, proteins, sugars, and lipids, all contain carbon. Also, the soft lead in your pencil, graphite, is also made up of carbon. The element in gold is of course, gold (Au). The most pure form of gold jewelry as you probably know is 24 karats meaning no other elements are present within the stone. Common impurities in lower karat gold include silver (Ag), copper(Cu), and palladium (Pd).

Rust is iron-oxide consisting of the elements iron and oxygen. When water touches an iron surface the water starts reacting with carbon dioxide in the air and forms carbonic acid, a weak acid. The presence of the acid causes the iron to dissolve. At the same time, the water starts breaking apart into oxygen and hydrogen. The oxygen from the breakdown of water reacts with the dissolved iron forming iron oxide, rust.

GOLD
Gold is an element, meaning that it consists only of one type of atom that cannot be chemically broken down into smaller parts. The only way to break gold down into smaller components would be through nuclear reactions that change the number of protons and electrons, the positively and negatively charged particles, inside the gold atoms.

The element gold is denoted by the symbol Au in the Periodic Table of Elements. Gold is characterized by having 79 protons and, in its elemental or uncharged state, also has 79 electrons. In its most common isotope, gold has 118 neutrons. Gold is typically found in nature in very small quantities mixed into a type of rock called ore, but can also be found in riverbed sediments.

DIAMONDS
Diamonds are composed almost entirely of the element carbon, often with some other impurities in them, such as nitrogen (i.e., pure diamonds are entirely carbon). The element carbon comes in three different natural forms, or allotropes: diamond, graphite, and amorphous. Although each of these forms is composed entirely of carbon, the carbon atoms are organized and bonded differently, creating unique properties for each.

Diamonds are formed under extreme pressure and heat, 100-200 kilometers below the Earth's surface, by bonding carbon into a three-dimensional crystal network. Diamonds are the hardest natural substance known to us. Graphite differs from diamonds in that the carbon atoms are bonded into flat sheets, creating a black, slippery substance that is one of the softest substances known to man. Graphite is what pencil lead is made out of. Amorphous carbon, otherwise known as soot, forms when a carbon-based material burns, or combusts, without enough oxygen to convert it completely to carbon dioxide.

Carbon is characterized by having 6 protons and 6 electrons, and usually 6 neutrons. This isotope of carbon is called carbon-12, with the number 12 referring to the atomic mass, or number of neutrons plus protons. Carbon also exists in the isotope carbon-14, with 8 neutrons, but this form is unstable (a radioactive isotope) and decays into nitrogen-14 over time by releasing an electron and converting a neutron into a proton. For more information about carbon, see this web page:
Carbon.

RUST
Rust is a molecule that is composed of two elements: iron (Fe, atomic number 26) and oxygen (O, atomic number 8). The chemical formula for rust is Fe₂O₃,which is called iron oxide, but is also known as ferric oxide or hematite, among other names. The word ferric refers to iron ions with a +3 charge (or with 23 electrons), whereas ferrous refers to iron ions with a +2 charge (or with 24 electrons). I think these words may have a Latin derivation, although I am not certain what their Latin meanings or root is.

Rust forms when the oxygen in air or in water combines with iron, which is a major component of steel, for example. Each oxygen atom essentially steals two electrons from the iron, forming oxygen atoms with a 2 charge (O-2 ions), while each iron atom donates three electrons to the oxygen, forming iron atoms with a +3 charge (Fe+3 ions, also known as ferric).

Since the oxygen ions are negatively charged and the iron ions are positively charged, they attract and create an ionic bond that forms rust. This type of reaction is known as a reduction-oxidation reaction, or a red-ox reaction, where oxygen is said to be reduced (hence the reduction, or decrease, in oxygens electric charge) and the iron is said to be oxidized by the oxygen. The chemical equation for the formation of rust is:

4(Fe) + 3(O₂) = 4(Fe⁺³) + 6(O^-2) = 2 (Fe₂O₃)