Where can I find information about "stone power" / lapidaire?

It is indeed difficult to find with a simple web-search reliable information about a scientifically mostly discredited idea, that nevertheless still enjoys enormous popularity in esoteric circles. Such a configuration seems to dominate the search algorithms. The French search term lapidaires is equally contaminated with very modern explanations about crafts in jewelry. To find more info one needs to search for "lapidary" in English and include terms like "magic".

In the thirteenth century an amazing development occurred in philosophy. Leading philosophers began to look at magic and its practices with different eyes than the ancient Church Fathers and distanced themselves from the devastating judgments of the older theorist of Christianity.
Between the time of Augustine and the High Middle Ages there was a significant upheaval in the assessment of this phenomenon. The new philosophers of the Latin West knew exactly what the influential clerical critics had to say about magic. Because they no longer let themselves be guided by earlier prejudices in forming their opinions, however, the term 'magic' stepped out of its negative aura and suddenly took on a more positive meaning.
_{–– Udo Reinhold Jeck: "Virtus Lapidum.- Zur Philosophischen Begründung Der Magischen Wirksamkeit Und Der Physikalischen Beschaffenheit Kostbarer Mineralien in Der Naturphilosophie Alberts Des Grossen", Early Science and Medicine, Volume 5: Issue 1, 2000.}

If "power of stones" is meant to be restricted to medical applications, then "lithothérapie" as a term seems to be an accepted French term, but in other languages seems to be reserved now for decidedly modern esoteric use. "Crystal healing" in English and "Heilsteine" (healing stones) in Germany would cover both historic and modern uses.

The term “lapidary medicine” does not appear in current historical surveys on the topic of medieval or early modern healing. It is a term I coined to define an idea and practice that played an integral role in pre-modern health care in the West, a practice that has thus far been largely ignored by researchers.
_{–– Nichola Erin Harris: "The Idea of Lapidary Medicine: Its Circulation and Practical Applications in Medieval and Early Modern England: 1000-1750", Dissertation, Rutgers, 2009.}

Christopher J. Duffin: "The western lapidary tradition in early geological literature: medicinal and magical minerals", Geology Today, Volume 21, Issue 2, Pages 58-63, 2005.

Francis Young: "A Medieval Book of Magical Stones: The Peterborough Lapidary", LuLu, 2016.

Claude Lecouteux: "A Lapidary of Sacred Stones: Their Magical and Medicinal Powers Based on the Earliset Sources", Simon and Schuster, 2012.

One thing to keep in mind is that most actually medieval sources will be more "integrative" than we like to see them. That means 'lapidary information' is mostly within other books, not even necessarily forming a separate chapter within them.

Further, what we now would probably 'clearly see' as separate attributes regarding these stones: giving 'invincibility' or 'power', or 'wealth', weren't distinct superstitions, but usually ones that came part and parcel with all other qualities in one package.

For example Paracelsus likes to hide his 'lapidary information' in his Philosophia:*

Since you are auditores, listen and learn: from both sides and take from it what is useful. Unless you ruminate daily on the things I tell you—how else would you arrive at the foundation of medicine? [How else] will you get to know the microcosmus in external nature, in which you will comprehend wonders and great secret things that reside within the human being. Do not do this for my sake, but for your own and for the patients and in order that God should be praised. For who until now has understood the human being as a human being? All the faculties are blind to him and do not recognize him, whence nothing but ruination results. Indeed, even the theologians would have to be meekly quiet, if they were to become physicians in this sense. The jurists would know what their cleverness amounts to, how it comes only from them, and so on and so on. All of this because the human being is taken up, and no one now wants to recognize him as he truly is. For you would [know] metal in water, as well as metal in earth, as well as in fire, as well as in air. You would know [four] forms of mercurius, four of betonica, four of tereniabin, four amethysts. Between all there is no difference except form. There are four chelidonia, and four orizon. All these things are no different [in external reality] than they are in the human being. For he too is created fourfold and well formed [in this regard]. The knowledge, art, and secret powers of the physician reside in this formation; and he should proceed accordingly, and not follow after any other profession; for they are not suitable for him in his affairs. With this I hope to have demostrated to you the first ground of medicine, with sufficient conviction that [you can see that] without philosophy there can be no such thing as a physician, but rather only impostures that grow like moss on the trunk of a tree.
_{–– Andrew Weeks: "Paracelsus (Theophrastus Bombastus von Hohenheim, 1493–1541). Essential Theoretical Writings", Aries Book Series – Texts and Studies in Western Esotericism, Vol 5, Brill: Leiden, Boston, 2008.
^{* "The First Foundation of Medicine"}}

An old German work would be Hermann Fühner: "Lithotherapie. Historische Studien über die medizinische Verwendung der Edelsteine", Dissertation, S Calvary: Berlin, 1902.

George Frederick Kunz: "The Curious Lore Of Precious Stones", Halcyon House: New York, 1938.

The always productive Hildegard von Bingen wrote Liber subtilitatum diversarum naturarum creaturarum (Physica), and from that we could extract:

Peter Riethe: "Hildegard von Bingen. Das Buch von den Steinen. Nach den Quellen übersetzt und erläutert von Peter Riethe", Otto Müller Verlag: Salzburg, ³1997.

The keywords under which these phenomena are analysed today include also "(western) esotericism", "magic", "amulets", "pendants" if the work is categorised in modern scholarship. Contemporary, especially later works against such practices and believes might of course include "witchcraft" as well. From the works below it becomes clear that well known medieval authors and titles of their works would be the easiest way to go.

Roberta Gilchrist: "Magic for the Dead? The Archaeology of Magic in Later Medieval Burials", Medieval Archaeology Volume 52, 2008 - Issue 1, 2013.

B. Ann Tlusty: "Invincible blades and invulnerable bodies: weapons magic in early-modern Germany", European Review of History: Revue européenne d'histoire, Volume 22, Issue 4: The History of Early Modern Masculinities; L'histoire des masculinités modernes, 2015.

John M. Riddle: "Lithotherapy in the Middle Ages…: Lapidaries Considered as Medical Texts", Pharmacy in History, Vol. 12, No. 2, pp. 39-50, 1970.

Not to overlook as an historical source are of course the remnants of these beliefs in fiction or poetic works:
Penelope B. R. Doob "Chaucer's Corones Tweyne and the Lapidaries", The Chaucer Review, Vol. 7, No. 2, pp. 85-96, 1972.

Marisa Galvez: "Dark Transparencies: Crystal Poetics in Medieval Texts and Beyond", Philological Quarterly, 2014. (PDF)

Karen Overbey: "Seeing through stone: Materiality and place in a medieval Scottish pendant reliquary", Res – Anthropology and aesthetics, Volume 65-66 | 2014/2015.

Ronnie H. Terpening: "The lapidary of L'intelligenza: Its literary background", Neophilologus, Volume 60, Issue 1, pp 75–88, 1976.

Gad Freudenthal and Jean-Marc Mandosio: "Old French into Hebrew in Twelfth-Century Tsarfat: Medieval Hebrew Versions of Marbode's Lapidary", Aleph, Vol. 14, No. 1, pp. 11-187, 2014.

J. Horace Nunemaker: "A Comparison of the Lapidary of Marbode with a Spanish Fifteenth-Century Adaptation", Speculum, Vol. 13, No. 1, pp. 62-67, 1938.

Katelyn Mesler: "The Medieval Lapidary of Techel/Azareus on Engraved Stones and Its Jewish Appropriations", Aleph Vol. 14, pp. 75-143, 2014.

The most famous lapidary of the medieval period may be that of Marbodius of Rennes.

John M. Riddle: "Marbode: De Lapidibus", Volumes 20-21 of Marbode of Rennes' De Lapidibus: Considered as a Medical Treatise with Text, Commentary, and C. W. King's Translation, Together with Text and Translation of Marbode's Minor Works on Stones, Marbode (Bishop of Rennes), Steiner, 1977.

De lapidis ou Liber lapidum, seu De gemmis, De lapidibus (avant 1090), in: Valérie Gontero-Lauze: "Sagesses minérales. Médecine et magie des pierres précieuses au Moyen Âge", Éditions Classiques Garnier: Paris, 2010, p151–176.

An older translation of Marbodius poems in the Liber Lapidum into French are online:

Poèmes de Marbode : évêque de Rennes (XIe siècle) / traduits en vers français, avec une introduction par Sigismond Ropartz Pagination avant numérisation : 227 pages. Reproduction numérique de l'édition imprimée à Rennes chez Verdier en 1873

From that an excerpt from the translation concerning diamonds, disregarding the poetic verse:

This stone is useful in the art of magic; It fills the heart with strength and energy; It can dispel tiring dreams, night ghosts, larvae and ghosts; Destroy poison the fatal influence, soothe conflicts and heal dementia: She knows how to avenge us on all our enemies. Put these precious gems on a bracelet, May the goldsmith set them in gold or silver; May this jewel always be placed in the sinister.

Quite an important medival German book, that not only lists but also explains the 'science' of stones to his readers would be Daz Steinbuoch by Volmar.

John Greenfield: "A Sermon on Stones? A Note on Volmar's Daz Steinbuoch", Linguas e Literaturas, 1995.
This introductory explanation seems necessary, for motivation, as the following old German text is not the easiest to read:

Volmar, Hans Lambel, St. Florianus, Heinrich: "Das Steinbuch: Ein altdeutsches Gedicht", G Henninger: Heilbronn, 1877.