Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

[EX Q]: Context: To understand minerals, we must first understand matter. Matter is the substance that physical objects are made of. The basic unit of matter is an atom. At the center of an atom is its nucleus. Protons are positively charged particles in the nucleus. Also in the nucleus are neutrons with no electrical charge. Orbiting the nucleus are tiny electrons. Electrons are negatively charged. An atom with the same number of protons and electrons is electrically neutral. If the atom has more or less electrons to protons it is called an ion. An ion will have positive charge if it has more protons than electrons. It will have negative charge if it has more electrons than protons. An atom is the smallest unit of a chemical element. That is, an atom has all the properties of that element. All atoms of the same element have the same number of protons. A molecule is the smallest unit of a chemical compound. A compound is a substance made of two or more elements. The elements in a chemical compound are always present in a certain ratio. Water is probably one of the simplest compounds that you know. A water molecule is made of two hydrogen atoms and one oxygen atom (Figure 3.2). All water molecules have the same ratio: two hydrogen atoms to one oxygen atom. A mineral is a solid material that forms by a natural process. A mineral can be made of an element or a compound. It has a specific chemical composition that is different from other minerals. One minerals physical properties differ from others. These properties include crystal structure, hardness, density and color. Each is made of different elements. Each has different physical properties. For example, silver is a soft, shiny metal. Salt is a white, cube- shaped crystal. Diamond is an extremely hard, translucent crystal. Minerals are made by natural processes. The processes that make minerals happen in or on the Earth. For example, when hot lava cools, mineral crystals form. Minerals also precipitate from water. Some minerals grow when rocks are exposed to high pressures and temperatures. Could something like a mineral be made by a process that was not natural? People make gemstones in a laboratory. Synthetic diamond is a common one. But that stone is not a mineral. It was not formed by a natural process. A mineral is an inorganic substance. It was not made by living organisms. Organic substances contain carbon. Some organic substances are proteins, carbohydrates, and oils. Everything else is inorganic. In a few cases, living organisms make inorganic materials. The calcium carbonate shells made by marine animals are inorganic. All minerals have a definite chemical makeup. A few minerals are made of only one kind of element. Silver is a mineral made only of silver atoms. Diamond and graphite are both made only of the element carbon. Minerals that are not pure elements are made of chemical compounds. For example, the mineral quartz is made of the compound silicon dioxide, or SiO2 . This compound has one atom of the element silicon for every two atoms of the element oxygen. Each mineral has its own unique chemical formula. For example, the mineral hematite has two iron atoms for every three oxygen atoms. The mineral magnetite has three iron atoms for every four oxygen atoms. Many minerals have very complex chemical formulas that include several elements. However, even in more complicated compounds, the elements occur in definite ratios. Minerals must be solid. For example, ice and water have the same chemical composition. Ice is a solid, so it is a mineral. Water is a liquid, so it is not a mineral. Some solids are not crystals. Glass, or the rock obsidian, are solid but not crystals. In a crystal, the atoms are arranged in a pattern. This pattern is regular and it repeats. Figure 3.3 shows how the atoms are arranged in halite (table salt). Halite contains atoms of sodium and chlorine in a pattern. Notice that the pattern goes in all three dimensions. The pattern of atoms in all halite is the same. Think about all of the grains of salt that are 
 Question: smallest particle of an element that has all the elements properties
[EX A]: atom

[EX Q]: Context: 35 Leukothea (/ljuki/ lew-KOTH-ee-, Greek: ) is a large, dark asteroid from the asteroid belt It was discovered by German astronomer Karl Theodor Robert Luther on April 19, 1855, and named after Leukothea, a sea goddess in Greek mythology. 
 Question: Who discovered the 35 Leukothea?
[EX A]: robert luther

[EX Q]: Context: ''Wolves Beyond the Border'' is one of the original stories by Robert E. Howard about Conan the Cimmerian, a fragment begun in the 1930s but not finished or published in Howard's lifetime. 
 Question: Who was Wolves Beyond the Border written by?
[EX A]:
robert e. howard