Fall for Autumn Gems
September 21, 2018
Nature gives us a brilliant palette of colour-changing leaves and a spectacular kaleidoscope of colourful sunsets during the autumn season. Yet, year-round, a treasure trove of gemstones in rich earth tones is ripe for collecting.
Let’s take a look at some gems, jewellery and minerals in autumnal hues to kick start this colourful season.
Natural, untreated topaz commonly occurs in pale yellow, brown, colourless or grey. Other hues of pink, green, blue and violet occur in nature, but these colours are rarely vivid. Although blue is the most popular colour of topaz, the most valuable are the orange, pink, red and purple colours generally referred to as Imperial topaz, which reflect the beauty of autumn sunsets.
Gemstone varieties are often named for something they resemble, such as sunstone, fire opal and fire agate, all colours in the autumnal spectrum.
Sunstone gets its phenomenon called aventurescence from tiny haematite, copper or goethite platelet inclusions that reflect light. The appearance of the phenomenon depends upon the size of the inclusions: small inclusions create a reddish or golden sheen on top of any bodycolour and larger inclusions create attractive, glittery reflections. Most sunstones have yellow, orange or brown bodycolour. Oregon is a major source of the finest sunstone.
Fire opals are found in a range of warm hues – red, orange and yellow. They can be transparent, translucent or opaque, usually with a vitreous lustre. According to Jürgen Schütz of Emil Weis Opals (Idar-Oberstein, Germany), one of the oldest opal cutting companies in the world, fire opal from Mexico is the only opal mined in quantity that is clear enough for faceting. It ranges from colourless to a dark red that is comparable with ruby. This type of material is available in large quantities and can even be calibrated. The majority of opal worldwide comes from Australia, Mexico and Ethiopia.
Fire agate is a variety of chalcedony, a micro or cryptocrystalline quartz. With its swirling flares of orange iridescence and flashing streaks of brown, yellow and green, it is aptly named. It forms in botryoidal structure, resembling a cluster of grapes. Fire agate is an excellent example of the iridescence phenomenon seen in chalcedony.
Agates can be found in the rich autumn colours of orange, brown and yellow, often forming in layers or bands of colour. Massive agate deposits were discovered in Rio Grande do Sul, Brazil in the 1800s and shipped for cutting to Idar-Oberstein. Today, agate from Brazil remains a favourite of gem carvers for its depth of colour.
October’s birthstones, opal and tourmaline, also offer a broad range of autumnal hues in yellow, orange and brown. Citrine and topaz, the November birthstones, fit well in this season’s theme, with yellow to red colour ranges.
Several other gemstones also convey the beauty and variety of autumnal colours:
Amber - Yellow and golden amber are most familiar to the consumer, although amber can be transparent red, which increases its value. Rare instances of strong fluorescence give amber a bluish or greenish appearance that increases its value even more. Its amorphous structure makes it a good medium for the preservation of plant and animal inclusions.
Citrine - Natural colour citrine is rare. Most of the citrine on the market is a result of the heat treatment of pale violet amethyst to an attractive yellow that makes it an appealing alternative to topaz and yellow sapphire.
Garnet - Several species of the garnet group also fall into the autumn colour range, the brightest being spessartine, which is typically yellowish orange through to reddish orange.
Pearls - Golden South Sea pearls are among the most desired pearls. They are grown in the gold-lip variety of the oyster Pinctada maxima, which gives them a thick nacre and warm, golden tones.
Sapphire - We usually think of sapphire as blue, even though sapphire comes in all colours and shades. The intense light to medium pinkish orange to orange-pink of Padparadscha sapphire is the rarest.
The bounty of autumn gemstones in a palette of brilliant coloured gemstones makes it fun to fall into the mood of the season.
Sharon Bohannon, a media editor who researches, catalogues and documents photos, is a GIA GG and GIA AJP. She works in the Richard T. Liddicoat Gemological Library and Information Center.