The Use of Stones and Crystals in Celtic Folklore 

   
In modern neopaganism and the new age movement using crystals and stones for healing is an almost ubiquitous practice. This can lead people who focus more on reconstruction to wonder what place this practice held, if any, with the ancients, in my case specifically the Irish and closely related Celtic cultures. When we look at the oldest sources, the accounts of the Greek and Roman writers all that is found is a reference to the fabled "Druid's Egg"*, an object that may or may not actually be a stone, said to be formed by the spit of snakes. On the otherhand when we look at slightly more recent folk practices from Ireland and Scotland we can find evidence of the use of stones and crystals for several purposes.
   Archeologists excavating Iron Age graves in England have found balls of "rock crystal" (clear quartz, I think) wrapped in bands of silver, or less often gold or bronze (Fraser Black, 1894). It is unknown what these were used for, whether they held a magical significance or were purely decorative, however similar balls of crystal were used in later periods in the belief that they could ensure victory in battle or bring healing. In Glenlyon there was such a wrapped crystal that was called either "Clach Bhaui" (powerful stone) or "Clach Buaidh" (victory stone); similarly another such stone is called the "Clach-na-Bratach" (stone of the standard) (Fraser Black, 1894).  The Clach-na-Bratach belongs to Clan Donnachaidh; it was found by the clan chief in 1315 on the way to battle and was believed to be a good omen, as such it was consulted before every following battle and carried into the fray until 1715 when an internal flaw noted (Fraser Black, 1894). After it was retired from battle it was noted that this stone also had healing powers especially for catle. There is also a named stone in Scotland called the Clach Dearg (red stone) which is reputed to have the ability to charge water with healing power, following a certain ritual process (Fraser Black, 1894). Some say the Clach Dearg was originally part of the wand of an arch Druid, while others believe it was imported from the east (McNeill, 1956). In Keppoch the MacKenzies are said to possess a healing stone associated with the holy well of Brighid, which would be dipped into the water from the well for a healing charm (McNeill, 1956). The majority of these stones range in size from one inch across to an inch and a half, and most are mounted with silver bands. 
   When used for healing purposes we see both the above described crystals and also references to similarly sized but more oval or egg shaped crystals being used. Cure stones might be used in one of two ways, either dipped in water which was then drunk or otherwise used on the afflicted perosn or animal, or rubbed directly on the injured or ill body part. When used in water the stone was often wrapped with silver bands, usually four, with a loop for hanging or wearing; the crystal would be dipped into water, while the person chanted:
   "Let me dip thee in the water
   Thou yellow, beautiful gem of power!
   In water of purest wave,
   Which Bridget didn't permit to be contaminated.
  In the name of the Apostles twelve,
  In the name of Mary, Virgin of virtues,
   And in the name of the High Trinity
   And all the shining angels,
  A blessing on the gem,
  A blessing in the water, and
  A healing of bodily ailments to each suffering creature." (Fraser Black, 1894)

 For my own purposes I prefer to use a slightly different version:
 "Let me dip you in the water
   You beautiful gem of power!
    In water of purest wave,
   Which Brighid kept pure.
  A blessing on the gem,
   A blessing in the water, and
  A healing of bodily ailments 
  to each suffering creature." 

 Besides these crystals there is also a history of the use of other types of stones for healing. Generally the type of stone didn't matter, as they appear to be simple river stones or pebbles, but often the color seemed to be significant, with white as the most common, and black, green, and red also described. While color is the most common descriptive point there are specific examples in Scottish Charms and Amulets of certain types of stone used for certain purposes:
    "Iron stone" (possibly hematite or iron ore?) - cure all, held
    Basalt - healing horses
     Jet - curing diseases
    Shale/Coal - holed, protecting animals from witchcraft
    Fossilized shells- arthritis
    Flint - general ailments
    Amber - general healing, cure for snake bites, used for people and animals
    Quartz - heal all, victory, cures infertility
    Both saints Columba and Fillan were said to possess "curing stones", all white, which could heal when dipped in water which was then consumed. Saint Molio also possessed such a healing stone, but that one was green and was rubbed on the afflicted area to effect a cure; interestingly this stone is also said to grant victory in battle and is alleged to have belonged to Clan McDonald. Many churches had healing stones on their altars, and some could be found next to holy wells; these might resemble the body part they were best used to heal, such as the eye or heart (McNeill, 1956). 
    In Scotland there are also accounts of several named curing stones: Clach Leigh (medicine stone) was a green tinged stone, Clach Ruaidhe (Red stone) was used for healing cows by rubbing it on the udder, and the Clach Spotaiche (spotted stone) was a piece of black basalt that was used in healing horses (Fraser Black, 1894). Whenever these or similar healing stones were used by rubbing  a charm might be said at the same time, such as this one from Strathspey:
  "Gu maith an diugh, 's fhearr am maireach;
   An deigh sin gun dad ach 'n larach." 
 (This day well, next better,
  After that nothing but a scar) - Fraser Black, 1894

A similar use can be seen in Irish lore, but instead of a known curing stone, all the person needs is to find three green stones in a running stream, after midnight but before dawn, and in silence. These stones are rubbed on the afflicted body part, from the top down towards the feet, while the person  chants:
   "Wear away, wear away,
    There you shall not stay,
    Cruel pain - away, away" (Wilde, 1896)

   Less commonly curing stones might be used for other purposes. A type of curing stone was one used for curing infertility. One example from Scotland is an egg shaped quartz that was passed from one "wise woman" to another upon death, and was used by placing the stone in running water (preferrably south-flowing) in which the woman would then wash her feet (Fraser Black, 1894). Stones of rock crystal would also be drilled to create a hole and then worn to protect against the evil eye (McNeill, 1956). The famed stone of the Brahan Seer was a white stone with a hole in it, said to be a gift of the fairies, through which he could divine the future (McNeill, 1956). 
   These stones are described as being worn and carried in the pocket, but may also recieve special care. One curing stone was said to be kept in a locked chest, wrapped in linen and then wool (Fraser Black, 1894). Another was said to be wrapped in cloth, kept in a silk bag, and wrapped in a napkin (Fraser Black, 1894). In many cases they were passed down in families as an heirloom, and if they were well known people might come from great distances away for the offered healing.

References:
Fraser Black, G., (1894). Scottish Charms and Amulets
McNeill, F., (1956). The Silver Bough, volume 1
 Wilde (1896). Irish Cures, Mystic Charms & Superstitions

*McNeill does reference "clach nathrach" (serpent stone) also called  a Druidical bead said to be created in the same way, by snakes, but found in Scotland on the ground, possibly referring to a common type of stone of an unknown (to me) type. This stone was used to protect against enchantments, for healing, and for childbirth.