This group has been named the Earth Signs because each of these signs has a cold and dry nature, in that these are the fundamental properties of the Earth Element. Their common characteristics are generally like the nature of Earth itself, and are shown through their practical, serious and quiet natures.
People born into Earth Signs tend to be careful about what they do, being concerned about their reputation and well-being.
The Earth Signs were originally known as the Capricorn Trigon. The three signs belonging to this Trigon are Capricorn, Taurus and Virgo. When three signs are 120 degrees apart from one another, or if you draw straight lines to connect them, and those lines form an Equilateral Triangle, they form a Trigon.
Unless there are astrological factors at play on the day of birth that prevent the Earth Element from expressing itself fully, Earth Sign people will tend to take solid and deliberate action toward achieving their goals. People born under Earth Signs are known for their ability to pursue material objectives with certainty and confidence. They don't become attached to others easily, and demonstrate their love through their actions, rather than their words.
Each of the Zodiac signs have characteristics that they don't share with the other signs of the same element, mostly due to the difference in Quadrature or Quality.
Capricorn, being the Cardinal Sign of the group, is the most ambitious of the Earth Signs, and tends to lead by example. Capricorn people generally possess a good deal of discipline, and tend to avoid doing whatever they consider to be unnecessary. They tend to be very reliable, and have a dislike for emotional display; they can't see the profit in it.
Taurus is the Fixed Sign, and tends to be very solid and practical in their behavior. They don't generally like a lot of noise and activity around them, and prefer home, tradition and nature for material and emotional support. They can, however, be rather stubborn at times.
Virgo is the Mutable Sign of the Trigon, and loves being useful. Many Virgos are known for their precision and attention to detail, and are happy to share their well-honed skills with others, but can be critical when they are trying to be of help.
As you probably have read before, the ancient philosophers regarded the equilateral triangle as a "pure" form; it was the basis of one of the 5 Platonic Solids. Because of this balance, signs that belong to the same Trigon are essentially one elemental unit, sharing the same characteristics. According to this kind of thinking, Capricorn should be a good match for Taurus or Virgo. But there are other factors in the vast realm of astrology that contribute to compatibility between people, who are not just their Zodiac Signs alone. The positions of the Moon and the planets at the time of birth, contribute to an almost infinite set of variations that modify the nature of everyone born under each sign.
Capricorn, Taurus and Virgo tend to do well with one another. Capricorn may put achievement above affection, whereas Taurus will often be uncompromising, especially with their partners. Virgo has a need for privacy that comes to the foreground every once and a while. The Earth Signs are known to get on famously, even more than members of the other Trigons do with each other.
All three Earth Signs are somewhat materialistic, but deal with it in very different ways. Capricorn considers material possessions and status as the source of security, whereas Taurus seeks it through stability and tradition. Virgo looks for security of the body and mind, and considers health as the most important possession one can acquire.
According to the conventional wisdom, the Earth Signs are generally compatible with the Water Signs, because the element of Water can nurture Earth. According to classical definitions, the Earth Signs are cold and dry, while the Water Signs are cold and wet; the coolness they have in common, and the moisture and dryness bring them into balance.
In other words, Capricorn, Taurus and Virgo are usually compatible with Cancer, Scorpio and Pisces. Nevertheless, this is a very general scheme of the Zodiac signs; sometimes Virgo may be frustrated by the lack of practical thinking of Pisces, or Capricorn could be irritated by Cancer's moodiness. Taurus may sometimes think that Scorpio is hiding something from them.
It should be clear that by the general, or archetypal scheme, the Earth Signs do well with one another, and share a natural compatibility with the Water Signs.