My first magatama was a jade bead purchased at Takachiho Jinja. Although magatama are made of various stones, I had a sense that jade is the most appropriate stone. Recently while conversing with a guji-san at a jinja he said that the only source of jade in Japan is Itoigawa in Niigata-ken. This was in connection with how people of the past avoided battle by negotiating and exchanging gifts such as jewelry. Here is some information which I have gathered about hisui jade and magatama beads. It turns out that jade is found in tectonic regions, and there are many stories about sacred sites in Japan being located on the Median Tectonic Line.
Magatama have long held deep spiritual meaning. The curved shape represents growth of a fetus, movement of the universe, the human soul. Magatama are comma-shaped beads which were made during the late Jomon period through the Kofun period, 1000 BCE to 600 CE. They were made of various stones and used as pendants and necklaces. By the end of the Kofun period they were mostly made of jade and used for ceremonial and religious purposes. They still possess a high symbolic value.
Jade and jadeite
—Jade is the gemstone name for two different mineral forms, Jadeite and Nephrite. [http://www.minerals.net/gemstone/jade_gemstone.aspx]
— Itoigawa is an important deposit of jadeite. [http://www.minerals.net/mineral/jadeite.aspx]
Itoigawa jadeite and magatama
‘The only source of jadeite in East Asia is from the Jade Coast in Niigata prefecture of Japan and known as “Itoigawa jade”… Itoigawa jadeite from Niigata is collected from the Hime River emptying onto the “Jade Coast” in the Japan Sea… Itoigawa jadeite was utilized in Japan from Jomon times, particularly in the 1st millennium BC. The ornaments of these hunter-gatherer-horticulturalists consisted of slit earrings and pebble pendants… In the Kofun period of state formation (250–645AD), curved beads became an important insignia of the elite, and the curved bead (magatama), bronze mirror and sword comprise the imperial regalia of the Japanese emperor.’ [Gina L. Barnes, http://www.academia.edu/11781202/JADE_its_tectonic_formation_geochemistry_and_archaeology_in_East_Asia_in_reverse_order]
Jade is produced by crustal movement, formed when a subducting plate is brought up to the surface by tectonic movements. An archaeological site from about 2,600 BCE has revealed that jade was processed in Itoigawa. Almost all of the jade artifacts of the Jomon culture were produced in Itoigawa, and not only distributed across the country but even to the Korean Peninsula. This makes this the oldest jade culture in the world. [http://www.globalgeopark.org/aboutGGN/list/Japan/6443.htm, http://www.geo-itoigawa.com/eng/geosite/geosite9/index.html ].
‘4000 BC Neolithic Jadeite culture in Japan! The Jadeite from the Itoigawa area was used in prehistoric times by people of the Jomon culture (4000 to 1600 BC) for fashioning first tools and then beads and pendants (taishu’s) and later on also the well known comma or cashew shaped Jade pendants or Magatamas. A Neolithic Jomon settlement has been excavated on Myama, a small hill overlooking Itoigawa City and all the artifacts assembled in a newly build museum the Chojagahara Archeology Hall. Jadeite use died out in Japan around 700 AD.’ [sic, Herbert Geiss, http://www.friendsofjade.org/current-article/2003/10/1/jade-news-fall-2003.html ]
Continental tectonic plates
The large map of the continental plates is from http://pubs.usgs.gov/gip/dynamic/slabs.html. The archipelago of Japan can be dimly seen on the upper left, where the (green) Eurasian plate meets the (brown) North American tectonic plate. Also seen bordering the (yellow) Pacific plate is the infamous Ring of Fire of volcanic activity.
中央構造線 （ちゅうおうこうぞうせん） Median Tectonic Line
The Median Tectonic Line of Japan is where the Eurasian and North American tectonic plates meet. [Ref. https://en.wikipedia.org/wiki/Japan_Median_Tectonic_Line ] The second map showing the Median Tectonic Line (red line) is from http://www.tohyamago.com/rekisi/chuoukouzousen_suwa/ . In this map, the Eurasian plate is pink and the North American plate is green. The Fossa Magna (shown in blue) is a zone of deformation and low topography.
Itoigawa is situated on the Japan Sea coast of Hokuriku Northlands. It is directly on the Itoigawa-Shizuoka portion of the Median Tectonic Line at the boundary where the Eurasian plate meets the Fossa Magna.
Median Tectonic Line and Sacred Sites
The geology of the ground on either side of the Median Tectonic Line differs greatly since they were created at different geological times. In some places the respective magnetic fields may cancel out, leaving a zero magnetic field at the interface.
Many sacred sites have been recognized on the Median Tectonic Line. See the third map showing sacred sites which is from https://www.facebook.com/yasuyuki.fujita1/posts/645751485489972 . They include, starting in the west (left):
Heitate Jingu on Mt. Aso, Kyushu Island
Ishizuchi Yama on Shikoku Island
Koyasan, Yoshino, and Ise Jingu on the Kii Peninsula
Suwa Taisha, Nagano Alps
Rieko Ido, Japanese history and anthropology researcher, has stated in this online article (no longer available), http://www.wattention.com/archives/japanese-sanctuaries-and-the-median-tectonic-line/:
‘Many famous Japanese shrines considered sacred since ancient times were built along this median tectonic line. One also cannot overlook the fact that rich minerals were deposited in the soil of median tectonic line because of repeated volcanic eruptions and earthquakes. Here we can see a strong relationship between Japanese sanctuaries and minerals. According to the old records. There used to be more eruptions and earthquakes in Japan. so it is easy to guess that the existence of many shrines built on the median tectonic line were closely related to religious faith in order to calm down eruptions and earthquakes. In fact, if you visit shrines. you will see that the gods enshrined in places of worship are most often symbols to quieten down the wrath of Nature.’
Further research is necessary in order to understand the relationship between tectonic lines and sacred sites. Still, isn’t it fitting that the hisui jadeite in magatama comes from a region associated with sanctuaries and sacred sites?
By YOICHI MASUDA/ Staff Writer, The Asahi Shimbun, September 25, 2016 at 16:30 JST
KANAZAWA–Stuck between a rock and a hard place, voters chose jade as Japan’s “national stone” over quartz. The selection was made here on Sept. 24  during the annual meeting of the Japan Association of Mineralogical Sciences. … because jade culture in Japan is the oldest in the world, having its roots about 7,000 years ago.
Summary of shrines shown in the last map:
1• 鹿島神宮 Kashima Shrine
2• 香取神宮 Katori Shrine
3• 諏訪大社 Suwa Taisha
4• 豊川稲荷 Toyokawa Inari
5• 豊川稲荷 Ise-Jingu
6• 天河大弁財天社 Tenkawa Dai Benzaiten Shrine
7• 高野山 Mt. Koya
8• 石鎚山 Mt. Ishizuchi