Gem Minerals

Gems are the most prized and famous of all minerals. All are better, clearer, or more crystalline forms of minerals which in common occurrences are less beautiful and less spectacular. Diamonds, emeralds, rubies, and sapphires stand out as the true gems. Other stones are classified as semiprecious and ornamental stones. Scarcity and fashion are important in determining the value of a gem, but the following physical properties are prized: luster, transparency, color, and hardness.

Luster depends on how light is reflected by the mineral. The transparent gems also refract or bend light and are cut to turn the light back into the observer’s eye. Color is essential in some gems, and incidental in others. It may add or detract greatly from the gem’s value. The harder the gem, the better it resists scratching of its polished surfaces. Here are some of the best-known gems and semiprecious stones. Many other minerals and some rocks are occasionally used as gems.

Exercise 2. Identify which gem stone is described

Gem	Hardness H.	Special Gravity Sp.Gr.
diamond	10	3,5
aquamarine	7,5 - 8
chrysoberyl	8,5	3,6
topaz	8	3,5
spinel	8	3,8

1. Emerald 2. Spinel 3. Zircon 4. Aquamarine 5. Topaz 6. Tourmaline

изумруд шпинель циркон аквамарин топаз турмалин

[’emər(ə)ld] [spi’nəl] [’zə:kɔn] [‚ækwəmə’ri:n] [’təupæz] [’təuməlin]

Text A. It is a light blue-green form of beryl (3BeO*Al2O3*6SiO2), only ore of the metal beryllium. H. 7.5 to 8. It also occurs as yellowish golden beryl. Found in many New England localities.

Text B.It is a form of beryl varying in color from light to deep green. Oriental stone, a green gem, is harder and may be the most valuable gem.

Text C.This stone is commonly black, forms long crystals, sometimes varicolored. Red, green, brown, and blue stones are known.

Text D.It is common in igneous rocks, but fairly rare as a gem stone. Clear brown crystals turn blue when heated and hence make better gems.

Text E.It sometimes reaches gem quality, the best red gems coming from Ceylon. Brown, green, and even blue stones occur. H. 8; Sp. Gr. 3.8.

Text F.It is a mineral of granites and other igneous rocks, is an alumino-fluoro-silicate. Large crystals have been found, some of gem quality. These are usually yellow, brown, or pink (when heated). H. 8; Sp. Gr. 3.5. False stone is brownish quartz.

Exercise 3. Find words, sentences and the text about “Transparent Gems”

Transparentgemsarestrikingfortheirlusterandbrillianceandoftenforhardnessandcolortoomostareoxidesofaluminumberylliumandmagnesiumsometimeswithsilicaallquartzgemsaresilicasometransparentgemsareidenticalmineralsthatdifferonlyincolorastherubyandthesapphiretransparencylackofflawscolorandsizedeterminethevalueofthesegems.

Exercise 4. Identify the form of Gerund