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What Is High Blood Pressure?

High blood pressure is a blood pressure reading of 140/90 mmHg or higher. Both numbers are important. About one in every four American adults has high blood pressure. Once high blood pressure develops, it usually lasts a lifetime. The good news is that it can be treated and controlled. High blood pressure is called 'the silent killer' because it ...

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WhatIsHighBloodPressure
Chemistry

Oil Viscosity

Everybody recognizes 'oil' as a word for liquid materials that do not behave like water. They have a 'thickness' and self-cohesive character (autocohesion) that enables them to form a film on a ... Continue reading

OilViscosity
Biology

The Human Pancreas

The pancreas is a body organ that does some heavy lifting. It carries on two important functions relating to digestion and the regulation of blood sugar. The exocrine, the larger function, makes ... Continue reading

HumanPancreas
Astronomy

Big Fish

The phrase 'big fish eat little fish' may hold true when it comes to planets and stars. Perhaps as many as 100 million of the sun-like stars in our galaxy harbor close-orbiting gas giant planets like ... Continue reading

BigFish
Chemistry

Why Does Cement Set?

Concrete has been known for literally thousands of years. It is a testament to the enduring strength of this material that concrete structures from those long-ago times are still standing strong ... Continue reading

WhyDoesCementSet

The Mineral Chalcedony

TheMineralChalcedonyChalcedony is a catch all term that includes many well known varieties of cryptocrystalline quartz gemstones. They are found in all 50 States, in many colors and color combinations, and in sedimentary, igneous, and metamorphic rocks. Chalcedony includes carnelian, sard, plasma, prase, bloodstone, onyx, sardonyx, chrysoprase, thundereggs, agate, flint, chert, jasper, petrified wood, and petrified dinosaur bone just to name a few of the better known varieties.

Because of its abundance, durability, and beauty, chalcedony was, except for sticks, animal skins, bones, plain rocks, and possibly obsidian, the earliest raw material used by humankind. The earliest recorded use of chalcedony was for projectile points, knives, tools, and containers such as cups and bowls. Early man made weapons and tools from many varieties of chalcedony including agate, agatized coral, flint, jasper, and petrified wood.

The move from using certain items as weapons and tools, to using the same items for ceremonial and personal adornment is very easily made. It was only natural for early man to use his finest looking knife for special occasions or to attach a special lance point or arrowhead to his tunic. In fact, agate and petrified wood may have simply been elevated to gems from common and functional weapons or tools. All 50 States produce some variety of chalcedony, but the material from some States is better known than that from others.