陳蕙雅思教材 - 雅思閱讀精選 (Topaz)

Topaz

Topaz is a hard,transparent mineral. It is a compound of aluminum, silica,

and fluorine. Gem topazis  valuable.    Jewelers call this variety  of the

stone "precioustopaz". The best-known precious topaz gems range in color

from rich yellow to lightbrown or pinkish red. Topaz is one of the hardest

gem minerals. In themineral table of       hardness, it has arating of 8, which

means that a knife cannotcut it, and that topaz will scratch quartz.

The golden variety ofprecious topaz is quite uncommon. Most of the world's

topaz is white or blue.The white and      blue crystals of topazare large,

often weighing thousandsof carats.        For this reason, thevalue of topaz

does not depend so muchon its size as it does with diamonds and many other

precious stones, wherethe  value increases about four timeswith each

doubling of weight. Thevalue of a topaz is largely determined by its

quality. But color is also important: blue topaz, for instance, isoften

irradiated to deepen andimprove its color.

Blue topaz is often soldas aquamarine and a variety of brown quartz is

widely sold as topaz. Thequartz is much           less brilliantand more plentiful

than true topaz. Most ofit is a variety of amethyst: that heat has turned

brown.

黃水晶

黃水晶是一種堅硬、透明的礦物質。 它是鋁、矽和氟的化合物。 黃水晶寶石價值不菲。 珠寶商把這種石頭稱為"黃玉"。

最出名的黃玉有各種顏色如深黃色、淡棕色、淺紅色等。 黃 水晶是最堅硬的寶石礦中的一種。  在礦石硬度表上，它的硬度為  8，這表明刀子不能割開

它而它可在石英上劃痕。 金黃色的黃玉品種非常罕見。 世界上大多數的黃水晶是白色或藍 色的。  這些白色或藍色的黃水晶晶體很大，常常有數千克拉重。  

由於這個原因，黃水晶的 價值不像鑽石和許多其它寶石那樣主要依賴於其大小，重量翻一番價值即上升約四倍。  黃

水晶的價值很大程度上取決於其品質，但顏色也很重要。  舉例來說，藍色的黃水晶常需放 射處理以加深和改善其顏色。  

藍色的黃水晶常被作為海藍寶石出售，許多種棕色石英被當 作黃水晶廣為販賣。 石英光亮度遠小於黃水晶，礦藏儲量也遠較黃水晶豐富。 大多數石英

是一種紫水晶，高溫使其變為棕色。