ROCKS AND MINERALSSCIENCE GRADE 7

MA. RACHEL B. ESPINOBuhatan National High SchoolPurok Marcos, Buhatan, Sorsogon City

WHAT IS A MINERAL? A mineral is a natural inorganic

substances with a definite chemical composition. It is found in the earth’s crust and does not come from living things. It is a naturally formed solid element or compound in which atoms and molecules are bound in together in a definite orderly arrangement to form crystals. Most of these crystals are too small to be seen even under a microscope. But some crystals are big enough to be identified.

Minerals are found in rocks. They appear like grains set firmly in a bed of rock. Some are dark and others are light in color. A rock may be composed of only one kind of mineral such as pure limestone, which is composed of calcite. Others may have more than one mineral like granite which has 3 very common minerals – quartz, feldspar and mica.

HOW CAN WE IDENTIFY MINERALS? Minerals are most easily identified by

their physical properties. These are:1. Hardness2. Color3. Streak4. Luster5. Cleavage and Fracture

HARDNESS Hardness is the resistance of a mineral

to scratching or abrasion. To test the hardness of a mineral sample, scratch it against another. That which can scratch by the other is softer.

Diamond is the hardest known mineral and is industrially used to cut or bore holes into glass, stone and other hard metals. Talc is the softest mineral used especially in making talcum powder.

COLOR Color is one way of

telling one mineral from another. It is their usually most noticeable and interesting property. But it is not the most reliable. The outside color of the mineral may have been changed by the atmosphere; hence, it is safe to examine the color of a fresh surface by breaking it apart.

A mineral may be translucent like mica, white or pink like quartz or lead gray like galena. Hematite is dark red while sulfur is yellow, while silver, tin and magnesium have almost the same gray-white color.

MICA QUARTZ GALENA

HEMATITESULFUR

SILVER

STREAK Streak refers to

the color of the powder a rock or mineral leaves behind when rubbed on a rough surface. The streak test consist of rubbing the mineral against a hard surface.

However, the color of the streak is not always the same as the color of the mineral. For example, the mineral pyrite which has the same color as gold leaves a greenish-black streak while gold always leaves a gold streak.

PYRITE

GOLD

The mineral hematite may be reddish brown or brownish black when viewed in solid form but is always cherry red in powder form, that is why hematite is also called bloodstone.

LUSTER Luster is the appearance of the surface

of a mineral in reflected light. A mineral that can reflect much light appears very shiny. Metals have metallic luster like silver and gold. Nonmetals are dull such as quartz, mica or asbestos.

CLEAVAGE AND FRACTURE Cleavage and fracture

describe the way a mineral breaks. Any irregular break is termed a fracture while the tendency of a certain minerals to break along one or more planes when put under pressure is called cleavage. Minerals split horizontally into thin sheets. Feldspar splits at nearly right angles in different directions.

FELDSPAR COPPER

SULFUR

SALT

PHILIPPINE MINERAL RESOURCES The richness of the Philippines in terms

of mineral resources is being attributed to its location at the western fringes of so called Pacific Ring of Fire – a ground found to be superloaded with mineral deposits. Globally, we are rankes 5th as most mineralized country in the world.

The Philippines is situated along the circum Pacific Ring of Fire where the processes of volcanism and plate convergence caused the deposition of minerals, both metallic and non-metallic. In fact, the large reserves of various kind of minerals beneath our ground has put the country in the world mineral map as 5th mineral country in the world, 3rd in gold reserves, 4th in copper and 5th in nickel.

Around 9 million hectares or 30% of the country’s total land area of 30 million hectares are believed to contain important metallic mineral deposits; while 5 million are also known to be potential site for nonmetallic reserves.

Among our important metallic minerals found in abundance in various parts of the country include gold, copper, iron, chromite, nickel, cobalt and platinum while our non-metallic resources include sand and gravel, limestone, marble, clay and other quarry materials.

The most prolific copper and gold products are found in Baguio and Mankayan district province of Benguet; although the Surigao-Davao district are also contributing much to Philippine gold production. Major producers of nickel are in Palawan and Surigao.

REFERENCES: Science Grade 7 Learners Module Integrated Science I Textbook Salandanan, Gloria G. Earth Science,

Quezon City: Phoenix Publishing House, 1988.

http://www.philippinestamps.net/RP2009-Minerals.htm

http://www.denr.gov.ph/news-and-features/latest-news/16-mineral-resources.html

http://nap.psa.gov.ph/peenra/results/mineral/default.asp